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Full text of "Everything Maths: Grade 11 Mathematics"

VERSION 0.9 NCS 

GRADE 11 
MATHEMATICS 

WRITTEN BY VOLUNTEERS 



SlYAVULA 

TECHNOLOGY-POWERED LEARNING 




I 








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SHUTTLEWORTH 

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Everything Maths 



Grade 1 1 Mathematics 



Version 0.9 - NCS 



by Siyavula and volunteers 



Copyright notice 



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Authors List 

This book is based upon the original Free High School Science Text which was entirely written 
by volunteer academics, educators and industry professionals. Their vision was to see a cur- 
riculum aligned set of mathematics and physical science textbooks which are freely available 
to anybody and exist under an open copyright license. 

Siyavula core team 

Neels van der Westhuizen; Alison Jenkin; Marina van Zyl; Helen Robertson; Carl Scheffler; Nicola du Toit; Leonard Gumani 
Mudau; 

Original Free High School Science Texts core team 

Mark Horner; Samuel Halliday; Sarah Blyth; Rory Adams; Spencer Wheaton 

Original Free High School Science Texts editors 

Jaynie Padayachee; Joanne Boulle; Diana Mulcahy; Annette Nell; Ren Toerien; Donovan Whitfield 

Siyavula and Free High School Science Texts contributors 

Sarah Abel; Dr. Rory Adams; Andrea Africa; Matthew Amundsen; Ben Anhalt; Prashant Arora; Amos Baloyi; Bongani Baloyi; 
Raymond Barbour; Caro-Joy Barendse; Richard Baxter; Tara Beckerling; Dr. Sarah Blyth; Sebastian Bodenstein; Martin Bongers; 
Gareth Boxall; Stephan Brandt; Hannes Breytenbach; Alex Briell; Wilbur Britz; Graeme Broster; Craig Brown; Richard Burge; 
Bianca Bhmer; George Calder-Potts; Eleanor Cameron; Richard Case; Sithembile Cele; Alice Chang; Richard Cheng; Fanny 
Cherblanc; Dr. Christine Chung; Brett Cocks; Stefaan Conradie; Rocco Coppejans; Tim Craib; Andrew Craig; Tim Crombie; 
Dan Crytser; Dr. Anne Dabrowski; Laura Daniels; Gareth Davies; Jennifer de Beyer; Jennifer de Beyer; Deanne de Bude; Mia 
de Vos; Sean Dobbs; Buhle Donga; William Donkin; Esmi Dreyer; Nicola du Toit; Matthew Duddy; Fernando Durrell; Dr. 
Dan Dwyer; Alex Ellis; Tom Ellis; Andrew Fisher; Giovanni Franzoni; Nina Gitau Muchunu; Lindsay Glesener; Kevin Godby; 
Dr. Vanessa Godfrey; Terence Goldberg; Dr. Johan Gonzalez; Saaligha Gool; Hemant Gopal; Dr. Stephanie Gould; Umeshree 
Govender; Heather Gray; Lynn Greeff; Carine Grobbelaar; Dr. Tom Gutierrez; Brooke Haag; Kate Hadley; Alex Hall; Dr. Sam 
Halliday; Asheena Hanuman; Dr. Nicholas Harrison; Neil Hart; Nicholas Hatcher; Jason Hayden; Laura Hayward; Cho Hee 
Shrader; Dr. Fritha Hennessy; Shaun Hewitson; Millie Hilgart; Grant Hillebrand; Nick Hobbs; Chris Holdsworth; Dr. Benne 
Holwerda; Dr. Mark Homer; Robert Hovden; Mfandaidza Hove; Jennifer Hsieh; Laura Huss; Dr. Matina J. Rassias; Rowan 
Jelley; Grant Jelley; Clare Johnson; Luke Jordan; Tana Joseph; Dr. Fabian Jutz; Brian Kamanzi; Dr. Lutz Kampmann; Simon 
Katende; Natalia Kavalenia; Nothando Khumalo; Paul Kim; Dr. Jennifer Klay; Lara Kruger; Sihle Kubheka; Andrew Kubik, 
Dr. Jannie Leach; Nkoana Lebaka; Dr. Tom Leinster; Henry Liu; Christopher Loetscher; Mike Loseby; Amandla Mabona, 
Malothe Mabutho; Stuart Macdonald; Dr. Anton Machacek; Tshepo Madisha; Batsirai Magunje; Dr. Komal Maheshwari 
Michael Malahe; Masoabi Malunga; Masilo Mapaila; Bryony Martin; Nicole Masureik; John Mathew; Dr. Will Matthews 
Chiedza Matuso; JoEllen McBride; Dr Melanie Dymond Harper; Nikolai Meures; Riana Meyer; Filippo Miatto; Jenny Miller 
Abdul Mirza; Mapholo Modise; Carla Moerdyk; Tshwarelo Mohlala; Relebohile Molaoa; Marasi Monyau; Asogan Moodaly, 
Jothi Moodley; Robert Moon; Calvin Moore; Bhavani Morarjee; Kholofelo Moyaba; Kate Murphy; Emmanuel Musonza; Tom 
Mutabazi; David Myburgh; Kamie Naidu; Nolene Naidu; Gokul Nair; Vafa Naraghi; Bridget Nash; Tyrone Negus; Huw 
Newton-Hill; Buntu Ngcebetsha; Dr. Markus Oldenburg; Thomas ODonnell; Dr. William P. Heal; Dr. Jaynie Padayachee; 
Poveshen Padayachee; Masimba Paradza; Dave Pawson; Justin Pead; Nicolette Pekeur; Sirika Pillay; Jacques Plaut; Barry 
Povey; Barry Povey; Andrea Prinsloo; Joseph Raimondo; Sanya Rajani; Alastair Ramlakan; Dr. Jocelyn Read; Jonathan Reader; 
Jane Reddick; Dr. Matthew Reece; Razvan Remsing; Laura Richter; Max Richter; Sean Riddle; Dr. David Roberts; Christopher 
Roberts; Helen Robertson; Evan Robinson; Raoul Rontsch; Dr. Andrew Rose; Katie Ross; Jeanne-Mari Roux; Mark Roux; 
Bianca Ruddy; Nitin Rughoonauth; Katie Russell; Steven Sam; Dr. Carl Scheffler; Nathaniel Schwartz; Duncan Scott; Helen 
Seals; Relebohile Sefako; Prof. Sergey Rakityansky; Sandra Serumaga-Zake; Paul Shangase; Cameron Sharp; Ian Sherratt; Dr. 
James Short; Roger Sieloff; Brandon Sim; Bonga Skozana; Clare Slotow; Bradley Smith; Greg Solomon; Nicholas Spaull; Dr. 
Andrew Stacey; Dr. Jim Stasheff; Mike Stay; Mike Stringer; Masixole Swartbooi; Tshenolo Tau; Tim Teatro; Ben Tho.epson; 
Shen Tian; Xolani Timbile; Robert Torregrosa; Jimmy Tseng; Tim van Beek; Neels van der Westhuizen; Frans van Eeden; Pierre 
van Heerden; Dr. Marco van Leeuwen; Marina van Zyl; Pieter Vergeer; Rizmari Versfeld; Mfundo Vezi; Mpilonhle Vilakazi; 
Ingrid von Glehn; Tamara von Glehn; Kosma von Maltitz; Helen Waugh; Leandra Webb; Dr. Dawn Webber; Michelle Wen; 
Dr. Alexander Wetzler; Dr. Spencer Wheaton; Vivian White; Dr. Gerald Wigger; Harry Wiggins; Heather Williams; Wendy 
Williams; Julie Wilson; Timothy Wilson; Andrew Wood; Emma Wormauld; Dr. Sahal Yacoob; Jean Youssef; Ewald Zietsman 



Everything Maths 



Mathematics is commonly thought of as being about numbers but mathematics is actually a language! 
Mathematics is the language that nature speaks to us in. As we learn to understand and speak this lan- 
guage, we can discover many of nature's secrets. Just as understanding someone's language is necessary 
to learn more about them, mathematics is required to learn about all aspects of the world - whether it 
is physical sciences, life sciences or even finance and economics. 

The great writers and poets of the world have the ability to draw on words and put them together in ways 
that can tell beautiful or inspiring stories. In a similar way, one can draw on mathematics to explain and 
create new things. Many of the modern technologies that have enriched our lives are greatly dependent 
on mathematics. DVDs, Google searches, bank cards with PIN numbers are just some examples. And 
just as words were not created specifically to tell a story but their existence enabled stories to be told, so 
the mathematics used to create these technologies was not developed for its own sake, but was available 
to be drawn on when the time for its application was right. 

There is in fact not an area of life that is not affected by mathematics. Many of the most sought after 
careers depend on the use of mathematics. Civil engineers use mathematics to determine how to best 
design new structures; economists use mathematics to describe and predict how the economy will react 
to certain changes; investors use mathematics to price certain types of shares or calculate how risky 
particular investments are; software developers use mathematics for many of the algorithms (such as 
Google searches and data security) that make programmes useful. 

But, even in our daily lives mathematics is everywhere - in our use of distance, time and money. 
Mathematics is even present in art, design and music as it informs proportions and musical tones. The 
greater our ability to understand mathematics, the greater our ability to appreciate beauty and everything 
in nature. Far from being just a cold and abstract discipline, mathematics embodies logic, symmetry, 
harmony and technological progress. More than any other language, mathematics is everywhere and 
universal in its application. 

See introductory video by Dr. Mark Horner: VMiwd at www.everythingmaths.co.za 



More than a regular textbook 



Mobile version 



PC and tablet version 



3, m J 



3 



Television broadcast 



Q. 






Video and rich media Practic self test 

look 



9 





9) 




Summary presentations Post and see questions 



Everything Maths is not just a Mathematics textbook. It has everything you expect from your regular 
printed school textbook, but comes with a whole lot more. For a start, you can download or read it 
on-line on your mobile phone, computer or iPad, which means you have the convenience of accessing 
it wherever you are. 

We know that some things are hard to explain in words. That is why every chapter comes with video 
lessons and explanations which help bring the ideas and concepts to life. Summary presentations at 
the end of every chapter offer an overview of the content covered, with key points highlighted for easy 
revision. 

All the exercises inside the book link to a service where you can get more practice, see the full solution 
or test your skills level on mobile and PC. 

We are interested in what you think, wonder about or struggle with as you read through the book and 
attempt the exercises. That is why we made it possible for you to use your mobile phone or computer 
to digitally pin your question to a page and see what questions and answers other readers pinned up. 



Everything Maths on your mobile or PC 

You can have this textbook at hand wherever you are - whether at home, on the the train or at school. 
Just browse to the on-line version of Everything Maths on your mobile phone, tablet or computer. To 
read it off-line you can download a PDF or e-book version. 

To read or download it, go to www.everythingmaths.co.za on your phone or computer. 





Using the icons and short-codes 

Inside the book you will find these icons to help you spot where videos, presentations, practice tools 
and more help exist. The short-codes next to the icons allow you to navigate directly to the resources 
on-line without having to search for them. 



(A1 23) Go directly to a section 

(►J (V123) Video, simulation or presentation 

QpS (P123) Practice and test your skills 

V?y (Q123) Ask for help or find an answer 



To watch the videos on-line, practise your skills or post a question, go to the Everything Maths website 
at www.everythingmaths.co.za on your mobile or PC and enter the short-code in the navigation box. 



Video lessons 



Look out for the video icons inside the book. These will take you to video lessons that help bring the 
ideas and concepts on the page to life. Get extra insight, detailed explanations and worked examples. 
See the concepts in action and hear real people talk about how they use maths and science in their 
work. 



See video explanation (^j (Video: V123) 





Video exercises 



Wherever there are exercises in the book you will see icons and short-codes for video solutions, practice 
and help. These short-codes will take you to video solutions of select exercises to show you step-by-step 
how to solve such problems. 



See video exercise (►) (Video: V123) 




You can get these videos by: 



• viewing them on-line on your mobile or computer 

• downloading the videos for off-line viewing on your phone or computer 

• ordering a DVD to play on your TV or computer 

• downloading them off-line over Bluetooth or Wi-Fi from select outlets 

To view, download, or for more information, visit the Everything Maths website on your phone or 
computer at www.everythingmaths.co.za 



Practice and test your skills 



One of the best ways to prepare for your tests and exams is to practice answering the same kind of 
questions you will be tested on. At every set of exercises you will see a practice icon and short-code. 
This on-line practice for mobile and PC will keep track of your performance and progress, give you 
feedback on areas which require more attention and suggest which sections or videos to look at. 



See more practice (A + ) (QM123) 




To practice and test your skills: 

Go to www.everythingmaths.co.za on your mobile phone or PC and enter the short-code. 



Answers to your questions 



Have you ever had a question about a specific fact, formula or exercise in your textbook and wished 
you could just ask someone? Surely someone else in the country must have had the same question at 
the same place in the textbook. 




GRADE 10 
MATHEMATICS 



(?) Help : 006d 



Factorise : L2k 2 j + 2ik 2 j 2 



• Is 12, k and j common factors? 

• Is it best to use k2j or kj2 as 
common factor? 

• What does factorise ean? 



MATHEMATICS I© "^ °° 6d 



Factorise : V2k 2 j + 24k 2 j 2 



Shud I devide out both k 
and j or just one? 



n 



You should take out all the 
common factors, so 12, k 2 and 
j because they appear in both 
terms 




Database of questions and answers 

We invite you to browse our database of questions and answer for every sections and exercises in the 
book. Find the short-code for the section or exercise where you have a question and enter it into the 
short-code search box on the web or mobi-site at www.everythingmaths.co.za or 
www.everythingscience.co.za. You will be directed to all the questions previously asked and answered 
for that section or exercise. 



(A1 23) Visit this section to post or view questions 
C?J (Q123) Questions or help with a specific question 



Ask an expert 



Can't find your question or the answer to it in the questions database? Then we invite you to try our 
service where you can send your question directly to an expert who will reply with an answer. Again, 
use the short-code for the section or exercise in the book to identify your problem area. 



Contents 




1 Introduction to the Book 2 

1.1 The Language of Mathematics 2 

2 Exponents 3 

2.1 Introduction 3 

2.2 Laws of Exponents 3 

2.3 Exponentials in the Real World 6 

3 Surds 9 

3.1 Introduction 9 

3.2 Surd Calculations 9 

4 Error Margins 18 

4.1 Introduction 18 

4.2 Rounding Off 18 

5 Quadratic Sequences 22 

5.1 Introduction 22 

5.2 What is a Quadratic Sequence? 22 

6 Finance 30 

6.1 Introduction 30 

6.2 Depreciation 30 

6.3 Simple Decay or Straight-line depreciation 31 

6.4 Compound Decay or Reducing-balance depreciation 34 

6.5 Present and Future Values of an Investment or Loan 37 

6.6 Finding i 38 

6.7 Finding n — Trial and Error 40 

6.8 Nominal and Effective Interest Rates 41 

6.9 Formula Sheet 46 

7 Solving Quadratic Equations 49 

7.1 Introduction 49 

7.2 Solution by Factorisation 49 

7.3 Solution by Completing the Square 53 

7.4 Solution by the Quadratic Formula 56 

7.5 Finding an Equation When You Know its Roots 61 

8 Solving Quadratic Inequalities 66 

8.1 Introduction 66 

8.2 Quadratic Inequalities 66 

12 



CONTENTS CONTENTS 

9 Solving Simultaneous Equations 72 

9.1 Introduction 72 

9.2 Graphical Solution 72 

9.3 Algebraic Solution 74 

10 Mathematical Models 78 

10.1 Introduction 78 

10.2 Mathematical Models 78 

10.3 Real-World Applications 79 

11 Quadratic Functions and Graphs 87 

11.1 Introduction 87 

1 1 .2 Functions of the Form y = a(x + p)' 1 + q 87 

12 Hyperbolic Functions and Graphs 96 

12.1 Introduction 96 

1 2.2 Functions of the Form y = -2 — \- q 96 

13 Exponential Functions and Graphs 103 

13.1 Introduction 103 

13.2 Functions of the Form y = ab {x+p) + q for b > 103 

14 Gradient at a Point 109 

14.1 Introduction 109 

14.2 Average Gradient 109 

15 Linear Programming 113 

15.1 Introduction 113 

15.2 Terminology 113 

15.3 Example of a Problem 115 

15.4 Method of Linear Programming 115 

15.5 Skills You Will Need 116 

16 Geometry 127 

16.1 Introduction 127 

16.2 Right Pyramids, Right Cones and Spheres 127 

16.3 Similarity of Polygons 131 

16.4 Triangle Geometry 133 

16.5 Co-ordinate Geometry 142 

16.6 Transformations 147 

17 Trigonometry 154 

17.1 Introduction 154 

17.2 Graphs of Trigonometric Functions 154 

17.3 Trigonometric Identities 163 

17.4 Solving Trigonometric Equations 175 

17.5 Sine and Cosine Identities 188 

13 



CONTENTS CONTENTS 

18 Statistics 198 

18.1 Introduction 198 

18.2 Standard Deviation and Variance 198 

18.3 Graphical Representation of Measures of Central Tendency and Dispersion 204 

18.4 Distribution of Data 208 

18.5 Scatter Plots 210 

18.6 Misuse of Statistics 213 

19 Independent and Dependent Events 218 

19.1 Introduction 218 

19.2 Definitions 218 



Introduction to the Book 





The Language of Mathematics m^BA 




The purpose of any language, like English or Zulu, is to make it possible for people to communicate. 
All languages have an alphabet, which is a group of letters that are used to make up words. There are 
also rules of grammar which explain how words are supposed to be used to build up sentences. This 
is needed because when a sentence is written, the person reading the sentence understands exactly 
what the writer is trying to explain. Punctuation marks (like a full stop or a comma) are used to further 
clarify what is written. 

Mathematics is a language, specifically it is the language of Science. Like any language, mathematics 
has letters (known as numbers) that are used to make up words (known as expressions), and sentences 
(known as equations). The punctuation marks of mathematics are the different signs and symbols that 
are used, for example, the plus sign (+), the minus sign (— ), the multiplication sign (x), the equals sign 
(=) and so on. There are also rules that explain how the numbers should be used together with the 
signs to make up equations that express some meaning. 

© See introductory video: VMinh at www.everythingmaths.co.za 



Exponents 





2. 1 Introduction 




In Grade 10 we studied exponential numbers and learnt that there are six laws that make working 
with exponential numbers easier. There is one law that we did not study in Grade 10. This will be 
described here. 

© See introductory video: VMeac at www.everythingmaths.co.za 




2.2 Laws of Exponents 




In Grade 10, we worked only with indices that were integers. What happens when the index is not an 
integer, but is a rational number? This leads us to the final law of exponents, 



(2.1) 




We say that x is an nth root of b if x n = b and we write x = \fb. n th roots written with the radical 
symbol, j~, are referred to as surds. For example, (— l) 1 = 1, so —1 is a i th root of 1. Using Law 6 
from Grade 10, we notice that 

(a » ) = a " = a (2.2) 

therefore a~ must be an nth root of a m . We can therefore say 

a% = sja~™ (2.3) 



For example, 



2" 



A number may not always have a real nth root. For example, if n = 2 and a = — 1, then there is no 
real number such that x 2 = — 1 because x 2 > for all real numbers x. 



2.2 CHAPTER 2. EXPONENTS 



Extension: 



Complex Numbers 



There are numbers which can solve problems like x 2 = — 1, but they are beyond the scope of 
this book. They are called complex numbers. 



It is also possible for more than one nth root of a number to exist. For example, (— 2) 2 = 4 and 2 2 = 4, 
so both —2 and 2 are 2 nd (square) roots of 4. Usually, if there is more than one root, we choose the 
positive real solution and move on. 



Example 1: Rational Exponents 



QUESTION 

Simplify without using a calculator: 



4- 1 -9- ] 



SOLUTION 



Step I : Rewrite negative exponents as numbers with positive indices 



Step 2 : Simplify inside brackets 



i _ i 

4 9 



_5_V 

9-4 
36 • 

1 ' 36 



= (6 2 )' 
Step 3 : Apply exponential Law 6 



CHAPTER 2. EXPONENTS 2.2 



Example 2: More rational Exponents 



QUESTION 


Simplify: 


(16x 4 )J 






SOLUTION 








Step 1 : Convert the number coefficient to a product of it's 


prime 


factors 




= (2V)I 






Step 2 : Apply exponential laws 


= 2 4x *.x 4x * 
= 2\x 3 
= 8x 3 









© See video: VMebb at www.everythingmaths.co.za 



Exercise 2-1 



Use all the laws to: 

1, Simplify: 

(a) (:r o ) + 5:r o -(0,25r o - 5 + 8i 

(b) S2 -I- S3 

(c) (64m 6 )§ 

... 12m 8 

(d) —-jr 
8m 9 

2. Re-write the following expression as a power of x: 



x\ x\ x\ X\/X 



2.3 CHAPTER 2. EXPONENTS 



A"y More practice Cwj video solutions f 9j or help at www.everythingmaths.co.: 



(1.)016e (2.) 016f 




2.3 Exponentials in the Real World 



EMBE 



In Grade 10 Finance, you used exponentials to calculate different types of interest, for example on a 
savings account or on a loan and compound growth. 



Example 3: Exponentials in the Real world 



QUESTION 



A type of bacteria has a very high exponential growth rate at 80% every hour. If there are 10 
bacteria, determine how many there will be in five hours, in one day and in one week? 



SOLUTION 



Step 1 : Population = Initial population x (1 + growf/j percentage)""" perlod "' hours 
Therefore, in this case: 
Papulation = 10(1,8)", where n = number of hours 

Step 2 : In 5 hours 

Population = 10(1,8) 5 = 189 

Step 3 : In 1 day = 24 hours 

Population = 10(1,8) 24 = 13 382 588 

Step 4 : in 1 week =168 hours 

Population = 10(l,8) 16s = 7,687 x 10 43 

Note this answer is given in scientific notation as it is a very big number. 



CHAPTER 2. EXPONENTS 2.3 



Example 4: More Exponentials in the Real world 



QUESTION 



A species of extremely rare, deep water fish has an very long lifespan and rarely has children. 
If there are a total 821 of this type of fish and their growth rate is 2% each month, how many 
will there be in half of a year? What will the population be in ten years and in one hundred 
years? 



SOLUTION 



Step 7 : Population = Initial population x (1+ growth percentage)' me period *" months 

Therefore, in this case: 

Population = 821(1,02)™, where n = number of months 

Step 2 : In half a year = 6 months 

Population = 821(1,02) 6 = 925 

Step 3 : In 10 years =120 months 

Population = 821(1,02) 120 = 8 838 

Step 4 : in 100 years = 1 200 months 

Population = 821(1,02) 1 20 ° = 1,716 x 10 13 
Note this answer is also given in scientific notation as it is a very big number. 



Chapter 2 



End of Chapter Exercises 



1. Simplify as far as possible: 

(a) 8-§ 

(b) ^16 + 8-* 

2. Simplify: 

a. (x 3 )t d. (-m 2 )i 

b. (s 2 )5 e. -(m 2 )3 

c. (m 5 )l f. (3?/i) 4 

3. Simplify as much as you can: 

3a" 2 6 15 c- 5 



2.3 



CHAPTER 2. EXPONENTS 



4. Simplify as much as you can: 



(9aV 



5. Simplify as much as you can: 

6. Simplify: 



3 3 \ 16 

a 2 6 4 



7. Simplify: 



/x 4 6 5 



8. Re-write the following expression as a power of x: 



X\ X\ X\/X\/X 



Vx~ 



f/Vj More practice f ►) video solutions Cfj or help at www.everythingmaths.co.za 



(1.)016g (2.)016h (3.)016i (4.) 01 6j (5.) 016k (6.) 016m 
(7.)016n (8.)016p 



Surds 





3. 1 Introduction 




In the previous chapter on exponents, we saw that rational exponents are directly related to surds. 
We will discuss surds and the laws that govern them further here. While working with surds, always 
remember that they are directly related to exponents and that you can use your knowledge of one to 
help with understanding the other. 

© See introductory video: VMebn at www.everythingmaths.co.za 




3.2 Surd Calculations 




There are several laws that make working with surds (or roots) easier. We will list them all and then 
explain where each rule comes from in detail. 

~~ (3.1) 

(3.2) 

(3.3) 



'a vb = 


= Vab 


nf® 


\/a 


V b 


Vb 




It is often useful to look at a surd in exponential notation as it allows us to use the exponential laws we 
learnt in Grade 10. In exponential notation, %/a = a» and s/b = 6«. Then, 



\favb 



a™ b" 
(ab)r> 
Vab 



(3.4) 



Some examples using this law: 



1. ^16 x yi 

= \M 

= 4 



2. V2 x v/32 
= ^64 



3.2 



CHAPTER 3. SURDS 



3. Va 2 b 3 X V fr 5 c 4 
= ab 4 c 2 



Surd Law 2: 



'a \/ a 



yi 



EMBI 



If we look at \f^ in exponential notation and apply the exponential laws then, 



ja la 

b \b 



(3.5) 



Vb 



Some examples using this law: 

1. VV2^V3 
= 2 

2. \/24 + ^3 
= 2 



3. VaW^^-VW 

= VaW 
= ab A 



Surd Law 3: yfa™ = a 1 



EMBJ 



If we look at \/a™ in exponential notation and apply the exponential laws then, 



U™ = (a m )- 



(3.6) 



For example, 



V¥ 



2" 

1 

22 

^2 



10 



CHAPTER 3. SURDS 3.2 




Two surds \/a and \/b are called like surds if m = n, otherwise they are called unlike surds. For 
example a/2 and \/3 are like surds, however \/2 and \/2 are unlike surds. An important thing to 
realise about the surd laws we have just learnt is that the surds in the laws are all like surds. 

If we wish to use the surd laws on unlike surds, then we must first convert them into like surds. In 
order to do this we use the formula 

sftfn = b \Ja hm (3.7) 



to rewrite the unlike surds so that bn is the same for all the surds. 



Example 1: Like and Unlike Surds 



QUESTION 

Simplify to like surds as far as possible, showing all steps: \/3 x \/5 

SOLUTION 

Step I : Find the common root 

= l V¥ x W 



Step 2 : Use surd Law 1 



V243 x 125 
^30375 



11 



3.2 CHAPTER 3. SURDS 



Simplest Surd Form W embl 



In most cases, when working with surds, answers are given in simplest surd form. For example, 

\/50 = V25 x 2 
= \/25 x V2 

= 5V2 

5V2 is the simplest surd form of \/50. 



Example 2: Simplest surd form 



QUESTION 



Rewrite vl8 in the simplest surd form: 



SOLUTION 



Step 1 : Convert the number 18 into a product of it's prime factors 



18 = V2 x 9 
= V2 x V¥ 



Step 2 : Square root all squared numbers: 

= 3^2 



Example 3: Simplest surd form 



12 



CHAPTER 3. SURDS 3.2 



QUESTION 


Simplify: VT47 + \/l08 










SOLUTION 










Step 1 : Simplify each 
factors 


square 


root by converting each number to 


a product of it's 


prime 


/108 = V49 x 3 + V36 x 3 


= V? 2 x 3 + \j&- x 3 


Step 2 : Square root all squared numbers 










= 7V3 + 6V3 






Step 3 : The exact same surds 


can be treated as "like terms" and 


may be added 








= 13^3 









© See video: VMecu at www.everythingmaths.co.za 



Rationalising Denominators wembm 



It is useful to work with fractions, which have rational denominators instead of surd denominators. It is 
possible to rewrite any fraction, which has a surd in the denominator as a fraction which has a rational 
denominator. We will now see how this can be achieved. 

Any expression of the form y'a+v^ (whereaand ft are rational) can be changed into a rational number 
by multiplying by sja — s/b (similarly *fa — \fb can be rationalised by multiplying by ,/a + \fb). This 
is because 

(sfti + Vb)(Va-Vb) =a-b (3.8) 

which is rational (since a and b are rational). 

If we have a fraction which has a denominator which looks like ^fa + \fb, then we can simply multiply 
the fraction by ^°LT ,- to achieve a rational denominator. (Remember that ^T t = 1) 

Vfi — vo \/a— Vb 

^-^ b x c - (3.9) 



\/a+Vb \fa-\fb \fa + \/b 

C\fa — cyb 
a — b 

13 



3.2 CHAPTER 3. SURDS 



or similarly 



s/a + Vb 



\fa — \/b y/a + \fb \fa — \/b 

C\fa + cvb 



(3.10) 



Example 4: Rationalising the Denominator 



QUESTION 



Rationalise the denominator of: 



SOLUTION 



Step / : Rationalise the denominator 

To get rid of yfx in the denominator, you can multiply it out by another sfx. This 
rationalises the surd in the denominator. Note that 4| = 1, thus the equation 
becomes rationalised by multiplying by 1 (although its' value stays the same). 

5x — 16 \fx 
x — 

Step 2 : Multiply out the numerators and denominators 

The surd is expressed in the numerator which is the preferred way to write ex- 
pressions. (That's why denominators get rationalised.) 

5xy/x — l&y/x 

x 
(y^)(5a - 16) 



Example 5: Rationalising the Denominator 



QUESTION 



Rationalise the following: 



SOLUTION 



vf-l° 



Step 1 : Rationalise the denominator 



14 



CHAPTER 3. SURDS 3.2 





5a -16 w ^y + W 
v^-10 " ^+10 








Step 2 


: Multiply out the numerators and denominators 

hx^/y - 16^7 + 5Cte - 160 
y- 100 










All the terms in the numerator are different and 
denominator does not have any surds in it anymore. 


cannot be 


simplified 


and the 





Example 6: 


Rationalise the 


denominator 








QUESTION 


Simplify the following: ^=|| 










SOLUTION 












Step 1 : 


Rationalise the denominator 












y-25 

Vv + 5 


s/y-s 

x 

Vv-5 






Step 2 : 


Multiply out the numerators and denominators 








V\/y - 25y^ - 
y-25 


by + 125 


y/y(y - 25) - 5(y - 

(y - 25) 

(2,-25)(^-25) 
(y - 25) 
= W-25 


-25) 





© See video: VMeea at www.everythingmaths.co.za 



Chapter 3 


End of Chapter Exercises 



15 



3.2 CHAPTER 3. SURDS 



1. Expand: 



2. Rationalise the denominator: 



3. Write as a single fraction: 



10 



3 r- 

2y/x 



4. Write in simplest su 


rd form: 


(a) 


Vf2 




(b) 


V45 + VSO 




(c) 


^48 
^12 




(d) 


\/l8^\/72 

V8 




(e) 
(f) 


4 

(V8-=-%/2) 

16 
(%/20 -=- -\/l2) 





5. Expand and simplify: 

6. Expand and simplify: 

7. Expand and simplify: 



(2 + V2) 2 
(2 + \/2)(l + VI) 



(l + %/3)(l + v / 8 + v / 3) 

8. Simplify, without use of a calculator: 

V5( V45 + 2v/80) 

9. Simplify: 

V98a; 6 + Vl28x 6 

10. Write the following with a rational denominator: 

^5 + 2 

1 1 . Simplify, without use of a calculator: 

V98-^8~ 



V50 

12. Rationalise the denominator: 

y — 4 

13. Rationalise the denominator: 

2x-20 



v/j/-vio 

i 



14. Evaluate without using a calculator: 12 . . „ 

1 5. Prove (without the use of a calculator) that: 

[% r /¥ AT 10^15 + 3^6 
V3 +5 V3-V6 = 6 



16 



CHAPTER 3. SURDS 



3.2 



16. The use of a calculator is not permissible in this question. Simplify completely by 
showing all your steps: 3~ 



\/l2- 



(3>/3) 



1 7. Fill in the blank surd-form number on the right hand side of the equation which 
make the following a true statement: — 3\/6 x — 2\/24 = — %/l8 x 



f/VM More practice f ►) video solutions (9) or help at www.everythingmaths.co.za 



(1.)016q (2.)016r (3.) 016s (4.)016t (5.)016u (6.)016v 
(7.)016w (8.)016x (9.)016y (10.)016z (11.) 0170 (12.) 0171 
(13.) 0172 (14.) 0173 (15.) 0174 (16.) 0175 (17.) 0176 



17 



Error Margins 





4. 1 Introduction 




When rounding off, we throw away some of the digits of a number. This means that we are making an 
error. In this chapter we discuss how errors can grow larger than expected if we are not careful with 
algebraic calculations. 

® See introductory video: VMefg at www.everythingmaths.co.za 




4.2 Rounding Off 




We have seen that numbers are either rational or irrational and we have see how to round off numbers. 
However, in a calculation that has many steps, it is best to leave the rounding off right until the end. 

For example, if you were asked to write 

3^3 + ^12 

as a decimal number correct to two decimal places, there are two ways of doing this as described in 
Table 4.1. 



Table 4.1: Two methods of writing 3i/3 + \/l2 as a decimal number. 



© Method 1 


© Method 2 


3^3 + . 


/12 = 3^3 + V4 . 3 


liv^+v^ = 3x1,73 + 3,46 




= 3^3 + 2^3 


= 5,19 + 3,46 




= 5^3 


= 8,65 




= 5x1,732050808... 






= 8,660254038... 






= 8,66 





Tip 



It is best to simplify all 
expressions as much as 
possible before round- 
ing off answers. This 
maintains the accuracy 
of your answer. 



In the example we see that Method 1 gives 8,66 as an answer while Method 2 gives 8,65 as an answer. 
The answer of Method 1 is more accurate because the expression was simplified as much as possible 
before the answer was rounded-off. 

In general, it is best to simplify any expression as much as possible, before using your calculator to 
work out the answer in decimal notation. 



18 



CHAPTER 4. ERROR MARGINS 4.2 



Example 1: Simplification and Accuracy 



QUESTION 



Calculate y 54 + v 16. Write the answer to three decimal places. 



SOLUTION 



Step 1 : Simplify the expression 



54 + ^16 = v/27.2 + W^2 

= ^27.^2+^8.^2 

= 3\ / 2 + 2v / 2 

= 5^2 

Step 2 : Convert any irrational numbers to decimal numbers 

5\/2 = 6,299605249... 

Step 3 : Write the final answer to the required number of decimal places. 

6,299605249 . . . = 6,300 (to three decimal places) 
54 + \/l& = 6,300 (to three decimal places). 



Example 2: Simplification and Accuracy 2 



QUESTION 



Calculate \/x + 1+ 1 \/{2x + 2) — (x + 1) ifx = 3,6. Write the answer to two decimal pla 



SOLUTION 



Step 1 : Simplify the expression 



19 



4.2 CHAPTER 4. ERROR MARGINS 



Vx+1 + - s/(2x + 2) - (x + 1) = <Jx + l + -\/2x + 2-x- 1 

= Vx + 1 + -\/r + 1 



Step 2 : Substitute the value of x into the simplified expression 



*Vx~+i = ^v/3^TT 



3 3 



2,859681412. 



Step 3 : Write the final answer to the required number of decimal places. 

2,859681412 . . . = 2,86 (To two decimal places) 
.-. a/e + 1 + | ■ s /(2x + 2) - {x + 1) = 2,86 (to two decimal places) if x = 3,6. 



Extension: 



Significant Figures 



In a number, each non-zero digit is a significant figure. Zeroes are only counted if they are 
between two non-zero digits or are at the end of the decimal part. For example, the number 
2000 has one significant figure (the 2), but 2000,0 has five significant figures. Estimating a 
number works by removing significant figures from your number (starting from the right) until 
you have the desired number of significant figures, rounding as you go. For example 6,827 
has four significant figures, but if you wish to write it to three significant figures it would mean 
removing the 7 and rounding up, so it would be 6,83. It is important to know when to estimate 
a number and when not to. It is usually good practise to only estimate numbers when it is 
absolutely necessary, and to instead use symbols to represent certain irrational numbers (such 
as 7r); approximating them only at the very end of a calculation. If it is necessary to approximate 
a number in the middle of a calculation, then it is often good enough to approximate to a few 
decimal places. 



Chapter 4 



End of Chapter Exercises 



1. Calculate: 

(a) \/l6\/72 to three decimal places 

(b) \/25 + a/2 to one decimal place 

(c) %/48\/3 to two decimal places 

(d) a/64 + \/l8\/l2 to two decimal places 



20 



CHAPTER 4. ERROR MARGINS 4.2 



(e) \f\ + v^^lS to six decimal places 

(f) \/3 + \fh\f§ to one decimal place 
2. Calculate: 

(a) Vx2 , if x = 3,3. Write the answer to four decimal places. 

(b) y/A + x , if x = 1,423. Write the answer to two decimal places. 

(c) \/x + 3 + y/x , if x = 5,7. Write the answer to eight decimal places. 

(d) \/2x5 + \yJx-\- 1 , if a; = 4,91. Write the answer to five decimal places. 

(e) ^/3xl + (4a; + 3)-\/x + 5 , if x = 3,6. Write the answer to six decimal places. 

(f) s /2x + 5(xl) + (5x + 2) + |V4 + x, if x = 1,09. Write the answer to one 
decimal place 

f/Vy More practice (►) video solutions Cc) or help at www.everythingmaths.co.za 
(1.)02sf (2.) 02sg 



21 



Quadratic Sequences 





5. 7 Introduction 




In Grade 1 you learned about arithmetic sequences, where the difference between consecutive terms 
is constant. In this chapter we learn about quadratic sequences, where the difference between consec- 
utive terms is not constant, but follows its own pattern. 

© See introductory video: VMeka at www.everythingmaths.co.za 




5.2 What is a Quadratic Sequence? 




DEFINITION: Quadratic Sequence 



A quadratic sequence is a sequence of numbers in which the second difference be- 
tween each consecutive term is constant. This called a common second difference. 



For example, 

1; 2; 4; 7; 11; ... (5.1) 

is a quadratic sequence, let us see why. 
The first difference is calculated by finding the difference between consecutive terms: 

1 2 4 7 11 

+ 1 +2 +3 +4 

We then work out the second differences, which are simply obtained by taking the difference between 
the consecutive differences {1; 2; 3; 4; . . .} obtained above: 

12 3 4 

\ / \ / \ / 

+1 +1 +1 

We then see that the second differences are equal to 1. Thus, Equation (5.1) is a quadratic sequence. 

Note that the differences between consecutive terms (that is, the first differences) of a quadratic se- 
quence form a sequence where there is a constant difference between consecutive terms. In the above 
example, the sequence of {1; 2; 3; 4; . . .}, which is formed by taking the differences between consec- 
utive terms of Equation (5.1), has a linear formula of the kind ax + b. 



Exercise 5-1 



The following are examples of quadratic sequences: 



22 



CHAPTER 5. QUADRATIC SEQUENCES 5.2 



2. 4; 9; 16; 25; 36; 



3. 7; 17; 31; 49; 71; 



4. 2; 10; 26; 50; 82; 



5. 31; 30; 27; 22; 15; ... 
Calculate the common second difference for each of the above examples. 

Qx*y More practice ( ►) video solutions (?) or help at www.everythingmaths.co.za 

(1.-5.) 01zm 

General Case 

If the sequence is quadratic, the n th term should be T n = an 2 + bn + c 

TERMS a + b + c 4a + 26 + c 9a + 3b + c 16a + 46 + c 

1 st difference 3a + 6 5a + 6 7a + 6 

2 nd difference 2a 2a 

In each case, the second difference is 2a. This fact can be used to find a, then 6 then c. 



Example 1: Quadratic sequence 



QUESTION 


Write down the next two terms and find a 


formula for the n" 


term of the 


sequence 5 


12; 23 


38;... 


SOLUTION 












Step 1 : Find the first differences between the terms 












5 12 
\ / \ 

+ 7 + 


23 
/ \ 

11 + 


38 
/ 

15 






i.e. 7; 11; 15. 













23 



5.2 CHAPTER 5. QUADRATIC SEQUENCES 



Step 2 : Find the second differences between the terms 



7 11 15 

\ / \ / 

+ 4 +4 

So the second difference is 4. 

Continuing the sequence, the differences between each term will be: 

...15 19 23... 

\ / \ / 

+ 4 +4 



Step 3 : Finding the next two terms 

The next two terms in the sequence will be: 



...38 57 80... 

\ / \ / 

+19 +23 



So the sequence will be: 5; 12; 23; 38; 57; 80. 

Step 4 : Determine values for a,b and c 

2a = 4 

which gives a = 2 

And 3a + b = 7 

.-. 3(2) + 6 = 7 

b = 7-6 

b = 1 

And a + 6 + c = 5 

.-. (2) + (l)+c = 5 

c = 5-3 

c = 2 

Step 5 : Find the rule by substitution 

T n = ax +bx + c 

:. T n = 2n 2 + n + 2 



Example 2: Quadratic Sequence 



21 



CHAPTER 5. QUADRATIC SEQUENCES 5.2 



QUESTION 



The following sequence is quadratic: 8; 22; 42; 68; . . . Find the rule. 



SOLUTION 



Step 1 : Assume that the rule is an 2 + bn + c 



TERMS 8 22 42 68 

\ / \ / \ / 

1 st difference +14 +20 +26 

\ / \ / 

2 nd difference +6 +6 



Step 2 : Determine values for a, b and c 



2a = 6 

which gives a = 3 

And 3a + 6 = 14 

.-. 9 + 6 = 14 

6 = 5 

And a + 6 + c = 8 

.-. 3 + 5 + c = 8 

c = 



Step 3 : Find the rule by substitution 



T„ = ax +bx + c 
T„ = 'in + 5n 



Step 4 : Check answer 

for 



n = 1, Ti = 3(1) 2 + 5(1) = 8 
n = 2, T 2 = 3(2) 2 + 5(2) = 22 
n = 3, T 3 = 3(3) 2 + 5(3) = 42 



Extension: 



Derivation of the n* -term of a Quadratic Sequence 



Let the n' h -term for a quadratic sequence be given by 

T„ = an + bn + c (5.2) 



2o 



5.2 CHAPTER 5. QUADRATIC SEQUENCES 

where a, 6 and c are some constants to be determined. 

T„ = an + bn + c 
Ti = a(l) 2 + 6(l) + c 

= a + 6 + c (5.3) 

T 2 = a(2) 2 + 6(2) + c 

= 4a + 26 + c (5.4) 

T 3 = a(3) 2 + 6(3) + c 

= 9a + 36 + c (5.5) 

The first difference (d) is obtained from 

Let d = Ti-Tx 
:. d = 'ia + b 

^b = d-3a (5.6) 

The common second difference (D) is obtained from 

D = (T 3 -T 2 )-(T 2 -T 1 ) 



(5a + 


!>) - (3a + 


la 




=> a 


D 


6 = d- 


-§•» 



(5.7) 



(5.8) 



Therefore, from (5.6), 

From (5.3), 

c = Ti - (a + 6) = Ti - — - d + | . D 

.:c = Ti+D-d (5.9) 

Finally, the general equation for the n' h -term of a quadratic sequence is given by 

T„ = -.n 2 + (d- |l?).n + (Ti - d + £>) (5.10) 



Example 3: Using a set of equations 



QUESTION 



Study the following pattern: 1; 7; 19; 37; 61; . . . 

?. What is the next number in the sequence? 

2. Use variables to write an algebraic statement to generalise the pattern. 

3. What will the 100" 1 term of the sequence be? 



26 



CHAPTER 5. QUADRATIC SEQUENCES 



5.2 



SOLUTION 



Step 1 : The next number in the sequence 

The numbers go up in multiples of 6 
1 + 6(1) = 7, then 7 + 6(2) = 19 
19 + 6(3) = 37, then 37 + 6(4) = 61 
Therefore 61 + 6(5) = 91 
The next number in the sequence is 91. 



Step 2 : Generalising the pattern 



TERMS 17 19 37 61 

1 st difference +6 +12 +18 +24 

\ / \ / \ / 



2 nd difference 



h6 



h6 



+6 



The pattern will yield a quadratic equation since the second difference is 
constant 

Therefore T„ = an 2 + bn + c 
For the first term: n = 1, then Ti = 1 
For the second term: n = 2, then T 2 = 7 
For the third term: n = 3, then T 3 = 19 
etc. 



Step 3 : Setting up sets of equations 



a + b + c = 


1 


...eqn(l) 


4a + 2b + c = 


7 


...eqn(2) 


9a + 36 + c = 


19 


...eqn(3) 



Step 4 : Solve the sets of equations 



eqn(2) — eqn(l) 
eqn(3) — eqn(2) 
eqn(5) — eqn(4) 



3a + 6 = 6 ...eqn(4) 

5a + 6= 12 ...eqn(5) 

2a = 6 
a = 3, b = —3 and c = 1 



Step 5 : Final answer 

The general formula for the pattern is T„ = 3n 2 — 3n + 1 



Step 6 : Term 100 

Substitute n with 100: 
3(100) 2 - 3(100) + 1 = 29 701 
The value for term 100 is 29 701. 



27 



5.2 



CHAPTER 5. QUADRATIC SEQUENCES 



Extension: 



Plotting a graph of terms of a quadratic sequence 



Plotting T„ vs. n for a quadratic sequence yields a parabolic graph. 
Given the quadratic sequence, 

3; 6; 10; 15; 21; ... 

If we plot each of the terms vs. the corresponding index, we obtain a graph of a parabola. 



Oio-- 



F-. 




Chapter 5 



End of Chapter Exercises 



1 . Find the first five terms of the quadratic sequence defined by: 

o„ = n + In + 1 

2. Determine which of the following sequences is a quadratic sequence by calculating 
the common second difference: 



(a) 6; 9; 14; 21; 


50; . . . 


(b) 1; 7; 17; 31; 49;... 


(c) 8; 17; 32; 53 


80;.. 


(d) 9; 26; 51; 84 


125;. 


(e) 2; 20; 50; 92 


146;. 


(f) 5; 19; 41; 71 


109;. 


(g) 2; 6; 10; 14; 


18; . . . 



28 



CHAPTER 5. QUADRATIC SEQUENCES 5.2 



(h) 3; 9; 15; 21; 27;... 
(i) 10; 24; 44; 70; 102;... 
(j) 1; 2,5; 5; 8,5; 13;... 
(k) 2,5; 6; 10,5; 16; 22,5;... 
(I) 0,5; 9; 20,5; 35; 52,5;... 

3. Given T n = 2n 2 , find for which value of n, T n = 242 

4. Given T„ = (n - 4) 2 , find for which value of n, T n = 36 

5. Given T„ = n 2 + 4, find for which value of n, T n = 85 

6. Given T„ = 3n 2 , find T n 

7. Given T„ = 7n 2 + An, find T 9 

8. Given T„ = An 2 + 3n - 1, find T 5 

9. Given T„ = l$n 2 , find T i0 

10. For each of the quadratic sequences, find the common second difference, the formula 
for the general term and then use the formula to find aioo- 

(a) 4; 7; 12; 19; 28;... 

(b) 2; 8; 18; 32; 50;... 

(c) 7; 13; 23; 37; 55;... 

(d) 5; 14; 29; 50; 77;... 

(e) 7; 22; 47; 82; 127;... 

(f) 3; 10; 21; 36; 55;... 

(g) 3; 7; 13; 21; 31;... 
(h) 3; 9; 17; 27; 39;... 

Q^J More practice IWJ video solutions CfJ or ne 'P at www.everythingmaths.co.za 

(1.) 0177 (2.) 0178 (3.) 0179 (4.) 017a (5.) 017b (6.) 017c 
(7.) 01 7d (8.) 01 7e (9.) 01 7f (1 0.) 01 7g 



2!) 



Finance 





6. 7 Introduction 




In Grade 10, the concepts of simple and compound interest were introduced. Here we will extend 
those concepts, so it is a good idea to revise what you've learnt. After you have mastered the techniques 
in this chapter, you will understand depreciation and will learn how to determine which bank is 
offering the best interest rate. 

© See introductory video: VMemn at www.everythingmaths.co.za 




6.2 Depreciation 




It is said that when you drive a new car out of the dealership, it loses 20% of its value, because it is 
now "second-hand". And from there on the value keeps falling, or depreciating. Second hand cars are 
cheaper than new cars, and the older the car, usually the cheaper it is. If you buy a second-hand (or 
should we say pre-owned\) car from a dealership, they will base the price on something called book 
value. 

The book value of the car is the value of the car taking into account the loss in value due to wear, age 
and use. We call this loss in value depreciation, and in this section we will look at two ways of how 
this is calculated. Just like interest rates, the two methods of calculating depreciation are simple and 
compound methods. 

The terminology used for simple depreciation is straight-line depreciation and for compound depre- 
ciation is reducing-balance depreciation. In the straight-line method the value of the asset is reduced 
by the same constant amount each year. In compound depreciation or reducing-balance the value of 
the asset is reduced by the same percentage each year. This means that the value of an asset does not 
decrease by a constant amount each year, but the decrease is most in the first year, then by a smaller 
amount in the second year and by an even smaller amount in the third year, and so on. 



Extension: 



Depreciation 



You may be wondering why we need to calculate depreciation. Determining the value of assets 
(as in the example of the second hand cars) is one reason, but there is also a more financial 
reason for calculating depreciation — tax! Companies can take depreciation into account as 
an expense, and thereby reduce their taxable income. A lower taxable income means that the 
company will pay less income tax to the Revenue Service. 



30 



CHAPTER 6. FINANCE 



6.3 




6.3 Simple Decay or Straight-line 
depreciation 



Let us return to the second-hand cars. One way of calculating a depreciation amount would be to 
assume that the car has a limited useful life. Simple depreciation assumes that the value of the car 
decreases by an equal amount each year. For example, let us say the limited useful life of a car is 5 
years, and the cost of the car today is R60 000. What we are saying is that after 5 years you will have 
to buy a new car, which means that the old one will be valueless at that point in time. Therefore, the 
amount of depreciation is calculated: 



R60 000 
5 years 



R12 000 per year. 



The value of the car is then: 



End of Year 1 
End of Year 2 
End of Year 3 
End of Year 4 
End of Year 5 



R60 000 - 1 x (R12 000) 
R60 000 - 2 x (R12 000) 
R60 000 - 3 x (R12 000) 
R60 000 - 4 x (R12 000) 
R60 000 - 5 x (R12 000) 



R48 000 
R36 000 
R24 000 
R12 000 
R0 



This looks similar to the formula for simple interest: 

Total Interest after n years = n x (P x i) 
where i is the annual percentage interest rate and P is the principal amount. 

If we replace the word interest with the word depreciation and the word principal with the words 
initial value we can use the same formula: 

Total depreciation after n years = n x (P x i) 

Then the book value of the asset after n years is: 

Initial Value - Total depreciation after n years = P — n x (P x i) 

A = P(l-nxi) 

For example, the book value of the car after two years can be simply calculated as follows: 

Book Value after 2 years = P(l — n x i) 

= R60 000(1 - 2 x 20%) 

= R60 000(1 - 0,4) 

= R60 000(0,6) 

= R36 000 

as expected. 

Note that the difference between the simple interest calculations and the simple decay calculations is 
that while the interest adds value to the principal amount, the depreciation amount reduces value! 



31 



6.3 CHAPTER 6. FINANCE 



Example 1: Simple Decay method 



QUESTION 



A car is worth R240 000 now. If it depreciates at a rate of 15% p.a. on a straight-line depreci- 
ation, what is it worth in 5 years' time? 



SOLUTION 



Step 1 : Determine what has been provided and what is required 

P = R240 000 

i = 0,15 

n = 5 

A is required 

Step 2 : Determine how to approach the problem 

A = P(l-ixn) 

A = 240 000(1- (0,15 x 5)) 

Step 3 : Solve the problem 

A = 240 000(1 - 0,75) 
= 240 000 x 0,25 
= 60 000 

Step 4 : Write the final answer 

In 5 years' time the car is worth R60 000 



Example 2: Simple Decay 



QUESTION 



A small business buys a photocopier for R12 000. For the tax return the owner depreciates this 
asset over 3 years using a straight-line depreciation method. What amount will he fill in on 



:S2 



CHAPTER 6. FINANCE 



6.3 



his tax form after 1 year, after 2 years and then after 3 years? 



SOLUTION 



Step 1 : Understanding the question 

The owner of the business wants the photocopier to depreciate to RO after 3 
years. Thus, the value of the photocopier will go down by 12 000 -j- 3 = R4 000 
per year. 

Step 2 : Value of the photocopier after 1 year 

12 000 - 4 000 = R8 000 

Step 3 : Value of the machine after 2 years 

8 000 - 4 000 = R4 000 

Step 4 : Write the final answer 

4 000 - 4 000 = 
After 3 years the photocopier is worth nothing 



Extension: 



Salvage Value 



Looking at the same example of our car with an initial value of R60 000, what if we suppose 
that we think we would be able to sell the car at the end of the 5 year period for R10 000? We 
call this amount the "Salvage Value". 

We are still assuming simple depreciation over a useful life of 5 years, but now instead 
of depreciating the full value of the asset, we will take into account the salvage value, and 
will only apply the depreciation to the value of the asset that we expect not to recoup, i.e. 
R60 000-R10 000 =R50 000. 

The annual depreciation amount is then calculated as (R60 000-R10 000)/5 =R10000 

In general, the formula for simple (straight line) depreciation: 



Annual Depreciation 



Initial Value - Salvage Value 
Useful Life 



Exercise 6-7 



1. A business buys a truck for R560 000. Over a period of 10 years the value of the truck depreciates 
to R0 (using the straight-line method). What is the value of the truck after 8 years? 

2. Shrek wants to buy his grandpa's donkey for R800. His grandpa is quite pleased with the offer, 
seeing that it only depreciated at a rate of 3% per year using the straight-line method. Grandpa 
bought the donkey 5 years ago. What did grandpa pay for the donkey then? 

3. Seven years ago, Rocco's drum kit cost him R12 500. It has now been valued at R2 300. What 
rate of simple depreciation does this represent? 

4. Fiona buys a DStv satellite dish for R3 000. Due to weathering, its value depreciates simply at 
15% per annum. After how long will the satellite dish be worth nothing? 



:',.', 



6.4 



CHAPTER 6. FINANCE 



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6.4 Compound Decay or 
Reducing-balance depreciation 




The second method of calculating depreciation is to assume that the value of the asset decreases at a 
certain annual rate, but that the initial value of the asset this year, is the book value of the asset at the 
end of last year. 

For example, if our second hand car has a limited useful life of 5 years and it has an initial value of 
R60 000, then the interest rate of depreciation is 20% (100%/S years). After 1 year, the car is worth: 

Book Value after first year = P(l — n x i) 

= R60 000(1 - 1 x 20%) 

= R60 000(1 - 0,2) 

= R60 000(0,8) 

= R48 000 

At the beginning of the second year, the car is now worth R48 000, so after two years, the car is worth: 



Book Value after second year 



P(l-n x i) 

R48 000(1 - 1 x 20%) 

R48 000(1 - 0,2) 

R48 000(0,8) 

R38 400 



We can tabulate these values. 



End of first year 
End of second year 
End of third year 
End of fourth year 
End of fifth year 



R60 000(1 - 1 x 20%) =R60 000(1 - 1 x 20%) 1 
R48 000(1 - 1 x 20%) =R60 000(1 - 1 x 20%) 2 
R38 400(1 - 1 x 20%) =R60 000(1 - 1 x 20%) 3 
R30 720(1 - 1 x 20%) =R60 000(1 - 1 x 20%) 4 
R24 576(1 - 1 x 20%) =R60 000(1 - 1 x 20%) 5 



R48 000,00 
R38 400,00 
R30 720,00 
R24 576,00 
R19 608,80 



We can now write a general formula for the book value of an asset if the depreciation is compounded. 
Initial Value - Total depreciation after n years = P(l — i) n (6.1) 

For example, the book value of the car after two years can be simply calculated as follows: 

Book Value after 2 years: A = P(l - i) n 

= R60 000(1 - 20%) 2 

= R60 000(1 - 0,2) 2 

= R60 000(0,8) 2 

= R38 400 

as expected. 

Note that the difference between the compound interest calculations and the compound depreciation 
calculations is that while the interest adds value to the principal amount, the depreciation amount 
reduces value! 



31 



CHAPTER 6. FINANCE 6.4 



Example 3: Compound Depreciation 



QUESTION 



The flamingo population of the Berg river mouth is depreciating on a reducing balance at a 
rate of 12% p. a. If there are now 3 200 flamingos in the wetlands of the Berg river mouth, how 
many will there be in 5 years' time? Answer to three significant figures. 



SOLUTION 



Step 1 : Determine what has been provided and what is required 

P = 3 200 

i = 0,12 

n = 5 

A is required 



Step 2 : Determine how to approach the problem 

A = P(l - i) n 

A = 3 200(1 - 0,12) 5 

Step 3 : Solve the problem 



A = 3 200(0,88) t> 
= 1688,742134 

Step 4 : Write the final answer 

There would be approximately 1 690 flamingos in 5 years' time. 



Example 4: Compound Depreciation 



QUESTION 



Farmer Brown buys a tractor for R250 000 which depreciates by 20% per year using the com- 
pound depreciation method. What is the depreciated value of the tractor after 5 years? 



:',.-, 



6.4 CHAPTER 6. FINANCE 



SOLUTION 


Step 1 


Determine what has been provided and what is 


required 






P = R250 000 

i = 0,2 

n = 5 
A is required 




Step 2 


Determine how to 


approach the problem 

a = p(i - if 

A = 250 000(1 - 0,2) 5 




Step 3 


Solve the problem 


A = 250 000(0,8) 5 
= 81 920 




Step 4 


Write the final answer 

Depreciated value after 5 years is R81 920 







Exercise 6-2 



1 . On January 1 , 2008 the value of my Kia Sorento is R320 000. Each year after that, the cars value 
will decrease 20% of the previous years value. What is the value of the car on January 1, 2012? 

2. The population of Bonduel decreases at a reducing-balance rate of 9,5% per annum as people 
migrate to the cities. Calculate the decrease in population over a period of 5 years if the initial 
population was 2 178 000. 

3. A 20kg watermelon consists of 98% water. If it is left outside in the sun it loses 3% of its water 
each day. How much does it weigh after a month of 31 days? 

4. A computer depreciates at x% per annum using the reducing-balance method. Four years ago 
the value of the computer was R10 000 and is now worth R4 520. Calculate the value of a; correct 
to two decimal places. 



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:«i 



CHAPTER 6. FINANCE 



6.5 




6.5 Present and Future Values of 
an Investment or Loan 



Now or Later 



EMBW 



When we studied simple and compound interest we looked at having a sum of money now, and 
calculating what it will be worth in the future. Whether the money was borrowed or invested, the 
calculations examined what the total money would be at some future date. We call these future 
values. 

It is also possible, however, to look at a sum of money in the future, and work out what it is worth 
now. This is called a present value. 

For example, if Rl 000 is deposited into a bank account now, the future value is what that amount will 
accrue to by some specified future date. However, if Rl 000 is needed at some future time, then the 
present value can be found by working backwards — in other words, how much must be invested to 
ensure the money grows to Rl 000 at that future date? 

The equation we have been using so far in compound interest, which relates the open balance (P), the 
closing balance (A), the interest rate (i as a rate per annum) and the term (n in years) is: 



P.(l + i)" 



(6.2) 



Using simple algebra, we can solve for P instead of A, and come up with: 

P = A.(l + i)- n 



(6.3) 



This can also be written as follows, but the first approach is usually preferred. 



P : 



(1 + i) n 



(6.4) 



Now think about what is happening here. In Equation 6.2, we start off with a sum of money and we 
let it grow for n years. In Equation 6.3 we have a sum of money which we know in n years time, and 
we "unwind" the interest — in other words we take off interest for n years, until we see what it is worth 
right now. 

We can test this as follows. If I have Rl 000 now and I invest it at 10% for 5 years, I will have: 

A = P.(l + i) n 

= Rl 000(1 + 10%) 5 
= Rl 610,51 

at the end. BUT, if I know I have to have R1610.51 in 5 years time, I need to invest: 

p = A.(i + iy" 

= Rl 610,51(1 + 10%r 5 
= Rl 000 

We end up with Rl 000 which — if you think about it for a moment — is what we started off with. Do 
you see that? 

Of course we could apply the same techniques to calculate a present value amount under simple 
interest rate assumptions — we just need to solve for the opening balance using the equations for 
simple interest. 



.37 



6.6 



CHAPTER 6. FINANCE 



Solving for P gives: 



P(l + i X n) 



(1 + ixn) 



(6.5) 



(6.6) 



Let us say you need to accumulate an amount of Rl 210 in 3 years time, and a bank 
account pays simple interest of 7%. How much would you need to invest in this bank 
account today? 



1 + n.i 

Rl 210 
1 + 3x7% 
= Rl 000 

Does this look familiar? Look back to the simple interest worked example in Grade 10. 
There we started with an amount of Rl 000 and looked at what it would grow to in 3 years' 
time using simple interest rates. Now we have worked backwards to see what amount we 
need as an opening balance in order to achieve the closing balance of Rl 210. 

In practise, however, present values are usually always calculated assuming compound interest. So 
unless you are explicitly asked to calculate a present value (or opening balance) using simple interest 
rates, make sure you use the compound interest rate formula! 



Exercise 6-3 



1. After a 20-year period Josh's lump sum investment matures to an amount of R313 550. How 
much did he invest if his money earned interest at a rate of 13,65% p. a. compounded half yearly 
for the first 10 years, 8,4% p. a. compounded quarterly for the next five years and 7,2% p. a. 
compounded monthly for the remaining period? 

2. A loan has to be returned in two equal semi-annual instalments. If the rate of interest is 16% per 
annum, compounded semi-annually and each instalment is Rl 458, find the sum borrowed. 



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6.6 Finding 




By this stage in your studies of the mathematics of finance, you have always known what interest rate 
to use in the calculations, and how long the investment or loan will last. You have then either taken 
a known starting point and calculated a future value, or taken a known future value and calculated a 
present value. 

But here are other questions you might ask: 

1. I want to borrow R2 500 from my neighbour, who said I could pay back R3 000 in 8 months 
time. What interest is she charging me? 



38 



CHAPTER 6. FINANCE 6.6 



2. I will need R450 for some university textbooks in 1,5 years time. I currently have R400. What 
interest rate do I need to earn to meet this goal? 

Each time that you see something different from what you have seen before, start off with the basic 
equation that you should recognise very well: 

A = P.{l + i) n 
If this were an algebra problem, and you were told to "solve for i", you should be able to show that: 

p = (1 + *)" 

You do not need to memorise this equation, it is easy to derive any time you need it! 
So let us look at the two examples mentioned above. 

1 . Check that you agree that P =R2 500, A =R3 000, n = ^ = |. This means that: 



3000 
2500 
= 0,314534... 

= 31,45% 
Ouch! That is not a very generous neighbour you have. 
2. Check that P =R400, A =R450, n = 1,5 

1../450 . 

1 = Vioo- 1 

= 0,0816871... 

= 8,17% 

This means that as long as you can find a bank which pays more than 8,17% interest, you should 
have the money you need! 

Note that in both examples, we expressed n as a number of years (^ years, not 8 because that is the 
number of months) which means i is the annual interest rate. Always keep this in mind — keep years 
with years to avoid making silly mistakes. 



Exercise 6-4 



1 . A machine costs R45 000 and has a scrap value of R9 000 after 10 years. Determine the annual 
rate of depreciation if it is calculated on the reducing balance method. 

2. After 5 years an investment doubled in value. At what annual rate was interest compounded? 



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3!) 



6.7 



CHAPTER 6. FINANCE 




6.7 Finding n — Trial and Error 




By this stage you should be seeing a pattern. We have our standard formula, which has a number of 
variables: 

A = P.(l + i)" 

We have solved for A (in Grade 1 0), P (in Section 6.5) and i (in Section 6.6). This time we are going to 
solve for n. In other words, if we know what the starting sum of money is and what it grows to, and if 
we know what interest rate applies — then we can work out how long the money needs to be invested 
for all those other numbers to tie up. 

This section will calculate n by trial and error and by using a calculator. The proper algebraic solution 
will be learnt in Grade 12. 



Solving for n, we can write: 



A = P(l + i) n 

A 

P 



(i + O" 



Now we have to examine the numbers involved to try to determine what a possible value of n is. Refer 
to your Grade 10 notes for some ideas as to how to go about finding n. 



Example 5: Term of Investment — Trial and Error 



QUESTION 


We invest R3 500 into a savings account which pays 7,5% compound interest for an 
period of time, at the end of which our account is worth R4 044,69. How long did 
the money? 


unknown 
we invest 


SOLUTION 










Step 1 : Determine what is 


given and what is required 






• P =R3 500 










• i = 7,5% 










• A =R4 044,69 










We are required to find n. 








Step 2 : Determine how to 

We know that: 


approach 

A 
A 
P 


the problem 

= P(l + i) n 
= (1 + 0" 







i() 



CHAPTER 6. FINANCE 



6.8 



Step 3 : Solve the problem 



R4 044,69 
R3 500 
1,156 



(i + 7,5%r 

(1,075)" 



We now use our calculator and try a few values for n. 



Possible n 


1,075" 


1,0 


1,075 


1,5 


1,115 


2,0 


1,156 


2,5 


1,198 



We see that n is close to 2. 



Step 4 : Write final answer 

The R3 500 was invested for about 2 years. 



Exercise 6-5 



1. A company buys two types of motor cars: The Acura costs R80 600 and the Brata R101 700, 
V.A.T. included. The Acura depreciates at a rate, compounded annually, of 15,3% per year and 
the Brata at 19,7%, also compounded annually, per year. After how many years will the book 
value of the two models be the same? 

2. The fuel in the tank of a truck decreases every minute by 5,5% of the amount in the tank at that 
point in time. Calculate after how many minutes there will be less than 30 I in the tank if it 
originally held 200/. 



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(1.)017v (2.)017w 




8 Nominal and Effective Interest 
Rates 



So far we have discussed annual interest rates, where the interest is quoted as a per annum amount. 
Although it has not been explicitly stated, we have assumed that when the interest is quoted as a per 
annum amount it means that the interest is paid once a year. 

Interest however, may be paid more than just once a year, for example we could receive interest on a 
monthly basis, i.e. 12 times per year. So how do we compare a monthly interest rate, say, to an annual 
interest rate? This brings us to the concept of the effective annual interest rate. 

One way to compare different rates and methods of interest payments would be to compare the closing 
balances under the different options, for a given opening balance. Another, more widely used, way is 



il 



6.8 



CHAPTER 6. FINANCE 



Tip 

Remember, the trick to 
using the formulae is to 
define the time period, 
and use the interest rate 
relevant to the time pe- 
riod. 



to calculate and compare the effective annual interest rate on each option. This way, regardless of the 
differences in how frequently the interest is paid, we can compare apples-with-apples. 

For example, a savings account with an opening balance of Rl 000 offers a compound interest rate of 
1% per month which is paid at the end of every month. We can calculate the accumulated balance 
at the end of the year using the formulae from the previous section. But be careful our interest rate 
has been given as a monthly rate, so we need to use the same units (months) for our time period of 
measurement. 

So we can calculate the amount that would be accumulated by the end of 1-year as follows: 



Closing Balance after 12 months 



Px (l + i) n 

Rl 000 x (1 + l%f 

Rl 126,83 



Note that because we are using a monthly time period, we have used n = 12 months to calculate the 
balance at the end of one year. 

The effective annual interest rate is an annual interest rate which represents the equivalent per annum 
interest rate assuming compounding. 

It is the annual interest rate in our Compound Interest equation that equates to the same accumulated 
balance after one year. So we need to solve for the effective annual interest rate so that the accumulated 
balance is equal to our calculated amount of Rl 126,83. 

We use lis to denote the monthly interest rate. We have introduced this notation here to distinguish 
between the annual interest rate, i. Specifically, we need to solve for i in the following equation: 

Px(l + i) 1 = Px(l + i 12 ) 12 

(l + ») = (l + «i 2 ) 12 divide both sides by P 

i = (1 + ii 2 ) 12 — 1 subtract 1 from both sides 

For the example, this means that the effective annual rate for a monthly rate i i2 = 1% is: 

i = (1 + ji 2 ) 12 -1 

= (1 + 1%) 12 - 1 

= 0,12683 

= 12,683% 

If we recalculate the closing balance using this annual rate we get: 



Closing Balance after 1 year 



Px (1+i)" 

Rl 000 x (1 + 12,683%)* 
Rl 126,83 



which is the same as the answer obtained for 12 months. 

Note that this is greater than simply multiplying the monthly rate by (12 x 1% = 12%) due to the effects 
of compounding. The difference is due to interest on interest. We have seen this before, but it is an 
important point! 



The General Formula 



EMBAA 



So we know how to convert a monthly interest rate into an effective annual interest. Similarly, we can 
convert a quarterly or semi-annual interest rate (or an interest rate of any frequency for that matter) into 
an effective annual interest rate. 



■12 



CHAPTER 6. FINANCE 



6.8 



For a quarterly interest rate of say 3% per quarter, the interest will be paid four times per year (every 
three months). We can calculate the effective annual interest rate by solving for i: 

P(l + i) = P(l + i A ) A 

where i& is the quarterly interest rate. 

So (1 + i) = (1,03) 4 , and so i = 12,55%. This is the effective annual interest rate. 

In general, for interest paid at a frequency of T times per annum, the follow equation holds: 

P(l + i) = P(l + i T ) T (6.7) 

where i T is the interest rate paid T times per annum. 



Decoding the Terminology 



EMBAB 



Market convention however, is not to state the interest rate as say 1% per month, but rather to express 
this amount as an annual amount which in this example would be paid monthly. This annual amount 
is called the nominal amount. 

The market convention is to quote a nominal interest rate of "12% per annum paid monthly" instead 
of saying (an effective) 1% per month. We know from a previous example, that a nominal interest 
rate of 12% per annum paid monthly, equates to an effective annual interest rate of 12,68%, and the 
difference is due to the effects of interest-on-i merest. 

So if you are given an interest rate expressed as an annual rate but paid more frequently than annual, 
we first need to calculate the actual interest paid per period in order to calculate the effective annual 
interest rate. 



monthly interest rate 



Nominal interest Rate per annum 



number of periods per year 
For example, the monthly interest rate on 12% interest per annum paid monthly, is: 

Nominal interest Rate per annum 



(6.8) 



monthly interest rate 



number of periods per year 

12% 



12 months 
= 1% per month 

The same principle applies to other frequencies of payment. 



Example 6: Nominal Interest Rate 



QUESTION 



Consider a savings account which pays a nominal interest at 8% per annum, paid quarterly. 
Calculate (a) the interest amount that is paid each quarter, and (b) the effective annual interest 
rate. 



13 



6.8 CHAPTER 6. FINANCE 



SOLUTION 



Step 7 : Determine what is given and what is required 

We are given that a savings account has a nominal interest rate of 8% paid 
quarterly. We are required to find: 

• the quarterly interest rate, i 4 

• the effective annual interest rate, i 



Step 2 : Determine how to approach the problem 

We know that: 

, . Nominal interest Rate per annum 

quarterly interest rate = , ; - 

number of quarters per year 

and 

P(l + i) = P(l + i T f 

where T is 4 because there are 4 payments each year. 
Step 3 : Calculate the monthly interest rate 

quarterly interest rate 



Nominal interest rate per annum 
number of periods per year 
8% 
4 quarters 
2% per quarter 



Step 4 : Calculate the effective annual interest rate 

The effective annual interest rate (i) is calculated as: 



(1+i) = 


= (i + uT 




(i + O = 


= (l + 2%) 4 




i - 


= (1 + 2%) 4 - 
= 8,24% 


-1 



Step 5 : Write the final answer 

The quarterly interest rate is 2% and the effective annual interest rate is 8,24%, 
for a nominal interest rate of 8% paid quarterly. 



11 



CHAPTER 6. FINANCE 6.8 



Example 7: Nominal Interest Rate 



QUESTION 



On their saving accounts, Echo Bank offers an interest rate of 18% nominal, paid monthly. If 
you save R100 in such an account now, how much would the amount have accumulated to in 
3 years' time? 



SOLUTION 



Step 1 : Determine what is given and what is required 

Interest rate is 18% nominal paid monthly. There are 12 months in a year. We 
are working with a yearly time period, so n = 3. The amount we have saved is 
R100, so P = 100. We need the accumulated value, A. 

Step 2 : Recall relevant formulae 
We know that 

,, . Nominal interest Rate per annum 

monthly interest rate = , ; : — , — - 

number of periods per year 

for converting from nominal interest rate to effective interest rate, we have 

l + i= {l + i T f 

and for calculating accumulated value, we have 

A = P x (l + i) n 

Step 3 : Calculate the effective interest rate 

There are 1 2 month in a year, so 

Nominal annual interest rate 







12 




18% 






12 




= 


1,5% 


per month 


and then, we have 






1 + 


i = 


(1 + * 12 ) 12 




i = 


(l + il 2 ) 12 -l 




= 


(1 + 1,5%) 12 - 1 




= 


(1,015) 12 -1 




= 


19,56% 



Step 4 : Reach the final answer 



A = Px(l + i) n 

= 100 x (1 + 19,56%) 3 

= 100 x 1,7091 

= 170,91 

45 



6.9 



CHAPTER 6. FINANCE 



Step 5 : Write the final answer 

The accumulated value 
cent.) 



s R170,91. (Remember to round off to the the nearest 



Exercise 6-6 



1. Calculate the effective rate equivalent to a nominal interest rate of 8,75% p.a. compounded 
monthly. 



2. Cebela is quoted a nominal interest rate of 9,15% per annum compounded every four months 
on her investment of R85 000. Calculate the effective rate per annum. 



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6.9 Formula Sheet 




As an easy reference, here are the key formulae that we derived and used during this chapter. While 
memorising them is nice (there are not many), it is the application that is useful. Financial experts are 
not paid a salary in order to recite formulae, they are paid a salary to use the right methods to solve 
financial problems. 



Definitions 



EMBAD 



Principal (the amount of money at the starting point of the calculation) 

interest rate, normally the effective rate per annum 

period for which the investment is made 

the interest rate paid T times per annum, i.e. i T = Nommal Interest Rate 



i(i 



CHAPTER 6. FINANCE 



6.9 



Equations 



EMBAE 



Simple Increase : A = P(l + i X n) 

Compound Increase : A = P{\ + i) n 

Simple Decay : A = P(l — i X n) 

Compound Decay : A = P(l — i) n 

Effective Annual Interest Rate{i) : (1 + i) = (1 + ir) 



Chapter 6 


End of Chapter Exercises 



1 . Shrek buys a Mercedes worth R385 000 in 2007. What will the value of the Mercedes 
be at the end of 201 3 if: 

(a) the car depreciates at 6% p.a. straight-line depreciation 

(b) the car depreciates at 12% p.a. reducing-balance depreciation. 

2. Greg enters into a 5-year hire-purchase agreement to buy a computer for R8 900. The 
interest rate is quoted as 11% per annum based on simple interest. Calculate the 
required monthly payment for this contract. 

3. A computer is purchased for R16000. It depreciates at 15% per annum. 

(a) Determine the book value of the computer after 3 years if depreciation is calcu- 
lated according to the straight-line method. 

(b) Find the rate, according to the reducing-balance method, that would yield the 
same book value as in 3a) after 3 years. 

4. Maggie invests R12 500,00 for 5 years at 12% per annum compounded monthly for 
the first 2 years and 14% per annum compounded semi-annually for the next 3 years. 
How much will Maggie receive in total after 5 years? 

5. Tintin invests R120000. He is quoted a nominal interest rate of 7,2% per annum 
compounded monthly. 

(a) Calculate the effective rate per annum correct to three decimal places. 

(b) Use the effective rate to calculate the value of Tintin's investment if he invested 
the money for 3 years. 

(c) Suppose Tintin invests his money for a total period of 4 years, but after 18 months 
makes a withdrawal of R20 000, how much will he receive at the end of the 4 
years? 

6. Paris opens accounts at a number of clothing stores and spends freely. She gets herself 
into terrible debt and she cannot pay off her accounts. She owes Hilton Fashion world 
R5 000 and the shop agrees to let Paris pay the bill at a nominal interest rate of 24% 
compounded monthly. 

(a) How much money will she owe Hilton Fashion World after two years? 

(b) What is the effective rate of interest that Hilton Fashion World is charging her? 



17 



6.9 CHAPTER 6. FINANCE 



Q\+) More practice f ►) video solutions Cfj or help at www.everythingmaths.co.za 



(1.) 01 7z (2.) 0180 (3.) 0181 (4.) 0182 (5.) 0183 (6.) 0184 



IS 



Solving Quadratic Equations 




7. 1 Introduction 




In Grade 10, the basics of solving linear equations, quadratic equations, exponential equations and 
linear inequalities were studied. This chapter extends that work by looking at different methods for 
solving quadratic equations. 

© See introductory video: VMemp at www.everythingmaths.co.za 




7.2 Solution by Factorisation 




How to solve quadratic equations by factorisation was discussed in Grade 10. Here is an example to 
remind you of what is involved. 



Example 1: Solution of Quadratic Equations 



QUESTION 


Solve the equation 2x 2 — 5x — 12 = 0. 






SOLUTION 






Step 1 


Determine whether the equation has common factors 

This equation has no common factors. 




Step 2 


Determine if the equation is in the form ax 2 

The equation is in the required form, with a 


+ bx + c 
= 2, b = - 


with a > 
-5andc= -12. 


Step 3 


Factorise the quadratic 

2x 2 — 5x — 12 has factors of the form: 

(2x + s)(x + v) 








with s and v constants to be determined. This 


multiplies out to 




2x + (s + 2v)x + sv 







• hi 



7.2 



CHAPTER 7. SOLVING QUADRATIC EQUATIONS 



We see that sv = — 12 and s + 2v = —5. This is a set of simultaneous equations 
in s and v, but it is easy to solve numerically. All the options for s and v are 
considered below. 



s 


V 


s + 2t) 


2 


-6 


-10 


-2 


6 


10 


3 


-4 


-5 


-3 


4 


5 


4 


-3 


-2 


-4 


3 


2 


6 


-2 


2 


-6 


2 


-2 



We see that the combination s = 3 and u = — 4 gives s + 2d = —5. 

Step 4 : Write the equation with factors 

(2x + 3)(x-4) = 

Step 5 : Solve the equation 

If two brackets are multiplied together and give 0, then one of the brackets must 
be 0, therefore 

2x + 3 = 

or 

x-4 = 

Therefore, x = — forz = 4 



Step 6 : Write the final answer 

The solutions to 2x 2 — 5x — 12 = are x = — | or x = 4. 



It is important to remember that a quadratic equation has to be in the form ax 2 + bx + c = before 
one can solve it using the factorisation method. 



Example 2: Solving quadratic equation by factorisation 



QUESTION 



Solve for a: a(a — 3) = 10 



SOLUTION 



Step I : Rewrite the equation in the form ax 2 + bx + c = 
Remove the brackets and move all terms to one side. 



50 



CHAPTER 7. SOLVING QUADRATIC EQUATIONS 7.2 

a - 3a - 10 = 
Step 2 : Factorise the trinomial 

(a + 2)(a-5) =0 
Step 3 : Solve the equation 

a + 2 = 

or 

a-5 = 

Solve the two linear equations and check the solutions in the original equation. 



Step 4 : Write the final answer 

Therefore, a = —2 or a = 5 



Example 3: Solving fractions that lead to a quadratic equation 



QUESTION 



Sobeforb: &+! = ■& 



SOLUTION 



Step 1 : Multiply both sides over the lowest common denominator 

36(6+l) + (6 + 2)(6 + l) = 4(6 + 2) 

(6 + 2)(6 + l) (6 + 2)(6+l) 

Step 2 : Determine the restrictions 

The restrictions are the values for b that would result in the denominator being 0. 
Since a denominator of would make the fraction undefined, 6 cannot be these 
values. Therefore, 6^—2 and 6^—1 

Step 3 : Simplify equation to the standard form 

The denominators on both sides of the equation are equal. This means we can 
drop them (by multiplying both sides of the equation by (b + 2)(6 + 1)) and just 
work with the numerators. 

36 2 + 36 + b 2 + 36 + 2 = 46 + 8 
46 2 + 26 - 6 = 
26 2 + 6 - 3 = 

Step 4 : Factorise the trinomial and solve the equation 



51 



7.2 



CHAPTER 7. SOLVING QUADRATIC EQUATIONS 



(26 + 3)(6-l) = 





26 + 3 = or 
b=— or 


6-1 = 
6= 1 


Step 5 : Check solutions in original equation 

Both solutions are valid 
Therefore, 6 = =^ or 6 = 1 







Exercise 7-1 



Solve 


the following quae 


ratic 


equations 


by 


factorisation. 


Some answers 


may 


be left in 


surd form 


1. 


2y 2 - 61 = 101 


















2. 


2?/ 2 - 10 = 


















3. 


y 2 - 4 = 10 


















4. 


2j/ 2 - 8 = 28 


















5. 


71/ 2 = 28 


















6. 


y 2 + 28 = 100 


















7. 


7i/ 2 + 14j/ = 


















8. 


12j/ 2 + 24?/ + 12 = 


= 
















9. 


16j/ 2 - 400 = 


















10. 


y 2 - 5y + 6 = 


















11. 


y 2 + 5j/ - 36 = 


















12. 


J/ 2 + 2y = 8 


















13. 


-j/ 2 - lly - 24 = 



















14. 


132/ - 42 = y 2 


















15. 


j/ 2 + 9j/ + 14 = 


















16. 


y 2 - 5ky + 4fc 2 = 



















17. 


y(2y + l) = 15 


















18. 


By , 3 i o — - 


-6 
















y-2 ^ v T y 2 


-2 II 




19. 


y-2 _ 2y + l 
y+i ~~ 1/-7 



















\Pc\ More practice (►) video solutions (9) or help at www.everythingmaths.co.za 



(1.) 0185 (2.) 0186 (3.) 0187 (4.) 0188 (5.) 0189 (6.) 018a 

(7.) 018b (8.) 018c (9.)018d (10.)018e (11.)018f (12.) 01 8g 

(13.) 018h (14.)018i (1 5.) 018j (16.) 018k (17.) 018m (18.)018n 
(19.)018p 



52 



CHAPTER 7. SOLVING QUADRATIC EQUATIONS 



7.3 




7.3 Solution by Completing the 
Square 



We have seen that expressions of the form: 

2 2 ,2 

Q X — 

are known as differences of squares and can be factorised as follows: 

(ax — b) (ax + b). 

This simple factorisation leads to another technique to solve quadratic equations known as completing 
the square. 

We demonstrate with a simple example, by trying to solve for x in: 

x 2 -2x-l = 0. (7.1) 

We cannot easily find factors of this term, but the first two terms look similar to the first two terms of 
the perfect square: 

(x- l) 2 =x 2 -2x + l. 

However, we can cheat and create a perfect square by adding 2 to both sides of the equation in (7.1) 
as: 



x 2 - 2x - 1 


= 


x 2 - 2x - 1 + 2 


= + 2 


x 2 - 2x + 1 


= 2 


(x-1) 2 


= 2 


(x - l) 2 - 2 


= 



Now we know that: 
which means that: 



2 = (\/2) 2 



(x-1) 2 -2 
is a difference of squares. Therefore we can write: 

(x - l) 2 - 2 = [(x - 1) - y/2][(x - 1) + V2] = 0. 

The solution to x 2 — 2x — 1 = is then: 

(ar - 1) - V2 = 

or 

(x - 1) + \/2 = 0. 

This means x = 1 + \/2 or x = 1 — \/2. This example demonstrates the use of completing the square 
to solve a quadratic equation. 

Method: Solving Quadratic Equations by Completing the Square 

1 . Write the equation in the form ax 2 + bx + c = 0. e.g. x 2 + 2x — 3 = 

2. Take the constant over to the right hand side of the equation, e.g. x 2 + 2x = 3 

3. Make the coefficient of the x 2 term = 1, by dividing through by the existing coefficient. 

4. Take half the coefficient of the x term, square it and add it to both sides of the equation, e.g. in 
x 2 + 2x = 3, half of the coefficient of the x term is 1 and l 2 = 1. Therefore we add 1 to both 
sides to get: x 2 + 2x + 1 = 3 + 1. 



53 



7.3 CHAPTER 7. SOLVING QUADRATIC EQUATIONS 



5. Write the left hand side as a perfect square: (x + l) 2 — 4 = 

6. You should then be able to factorise the equation in terms of difference of squares and then solve 
for x: 



[(x+l)-2][(x + l) + 2)} = 
(x-l)(x + 3) = 

.". x = 1 or x = —3 



Example 4: Solving Quadratic Equations by Completing the Square 



QUESTION 



Solve by completing the square: 

x 2 - lux- 11 = 



SOLUTION 



Step 1 : Write the equation in the form ax 2 + bx + c = 



Step 2 : Take the constant over to the right hand side of the equation 



Step 3 : Check that the coefficient of the x 2 term is 1. 

The coefficient of the x 2 term is 1. 



Step 4 : Take half the coefficient of the x term, square it and add it to both sides 

The coefficient of the x term is —10. Therefore, half of the coefficient of the x 
term will be % = ~ *> anc ' ^ e s q uare of it will be (— 5) 2 = 25. Therefore: 

x 2 - lCte + 25 = 11 + 25 



Step 5 : Write the left hand side as a perfect square 

(x-5) 2 -36 = 

Step 6 : Factorise equation as difference of squares 

(x-5) 2 -36 = 
[(x-5) + 6][(cc-5)-6] = 

Step 7 : Solve for the unknown value 



51 



CHAPTER 7. SOLVING QUADRATIC EQUATIONS 7.3 



(x + l)(x-ll) = 

.'. x = — 1 or i = ll 



Example 5: Solving Quadratic Equations by Completing the Square 



QUESTION 



Solve by completing the square: 

2x 2 - 8x - 16 = 



SOLUTION 



Step 1 : Write the equation in the form ax 2 + bx + c = 

2x 2 - 8x - 16 = 
Step 2 : Take the constant over to the right hand side of the equation 

2x 2 - 8a; = 16 

Step 3 : Check that the coefficient of the x 2 term is 1. 

The coefficient of the x 2 term is 2. Therefore, divide both sides by 2: 

x 2 - Ax = 8 



Step 4 : Take half the coefficient of the x term, square it and add it to both sides 

The coefficient of the x term is —4; ^^ = —2 and (— 2) 2 = 4. Therefore: 

x 2 -Ax + 4 = 8 + 4 



Step 5 : Write the left hand side as a perfect square 

(x-2) 2 - 12 = 
Step 6 : Factorise equation as difference of squares 

[(x - 2) + VV2] [(as - 2) - %/l2] = 
Step 7 : Solve for the unknown value 

[a;-2 + \/l2][a;-2-A/l2] = 

.-. x = 2 - \/l2 or x = 2 + ^/V2 

Step 8 : The last three steps can also be done in a different way 



55 



7.4 



CHAPTER 7. SOLVING QUADRATIC EQUATIONS 



Leave the left hand side written as a perfect square 

(x - 2) 2 = 12 

Step 9 : Take the square root on both sides of the equation 

x-2 = ±Vl2 



Step 1 : Solve for x 

Therefore x = 2 - vT2 or x = 2 + \/l2 
Compare to answer in step 7. 



See video: VMeyf at www.everythingmaths.co.za 



Exercise 7-2 



Solve the following equations by completing the square: 

1 . x 2 + lOx - 2 = 

2. x 2 + Ax + 3 = 

3. x 2 + 8x - 5 = 

4. 2x 2 + Vlx + 4 = 

5. a; 2 + 5a; + 9 = 

6. x 2 + 16x + 10 = 

7. 3x 2 + 6x - 2 = 

8. 2 2 +8z-6 = 

9. 2z 2 - llz = 
10. 5 + 4z-,z 2 =0 

fa+) More practice f ►) video solutions (9 J or help at www.everythingmaths.c 



(1.)018q (2.)018r (3.) 018s (4.)018t (5.)018u (6.)018v 
(7.)018w (8.)018x (9.)018y (10.)018z 




7.4 Solution by the Quadratic 
Formula 




EMBAI 



It is not always possible to solve a quadratic equation by factorising and sometimes it is lengthy and 
tedious to solve a quadratic equation by completing the square. In these situations, you can use the 
quadratic formula that gives the solutions to any quadratic equation. 



r.o 



CHAPTER 7. SOLVING QUADRATIC EQUATIONS 



7.4 



Consider the general form of the quadratic function: 

f(x) = ax + bx + c. 

Factor out the a to get: 

f(x)=a(x 2 + -x+-). (7.2) 

\ a a J 

Now we need to do some detective work to figure out how to turn (7.2) into a perfect square plus some 
extra terms. We know that for a perfect square: 



and 



(m + n) = m + 2mn + n 



/ \2 2 , 2 

(m — n) = m — Iran + n 



The key is the middle term on the right hand side, which is 2x the first term x the second term of the 
left hand side. In (7.2), we know that the first term is x so 2x the second term is -. This means that 
the second term is ^-. So, 



x + 



2ii 



2 „ b ( b 



In general if you add a quantity and subtract the same quantity, nothing has changed. This means if we 
add and subtract (^) from the right hand side of Equation (7.2) we will get: 



m 



a x H x H — 



a x -\ — x - 
a 



2a J 



b_y c 

2a I a 



2a J 



We set f(x) = to find its roots, which yields: 



' ,[X+ Ya) 



la 



4a 



Now dividing by a and taking the square root of both sides gives the expression 

b 



2a 



± 



Finally, solving for x implies that 



2a 
2a 



b 2 _c 
4a 2 a 



b 2 c 
4a 2 a 
b 2 - lac 



(7.3) 

(7.4) 

(7.5) 
(7.6) 

U.7) 
(7.8) 



which can be further simplified to: 



4o 2 

b ± Vb 2 - 4ac 
2a 



(7.9) 



These are the solutions to the quadratic equation. Notice that there are two solutions in general, but 
these may not always exists (depending on the sign of the expression b 2 — Aac under the square root). 
These solutions are also called the roots of the quadratic equation. 



57 



7.4 CHAPTER 7. SOLVING QUADRATIC EQUATIONS 



Example 6: Using the quadratic formula 



QUESTION 



Find the roots of the function f(x) = 2x 2 + 3x — 7. 



SOLUTION 



Step I : Determine whether the equation can be factorised 

The expression cannot be factorised. Therefore, the general quadratic formula 
must be used. 



Step 2 : Identify the coefficients in the equation for use in the formula 

From the equation: 

a = 2 

6 = 3 

c=-7 

Step 3 : Apply the quadratic formula 

Always write down the formula first and then substitute the values of a, b and c. 



-b ± Vb 2 - 4ac ,„.„, 

x = h- (7.10) 

2a 



-(3)±V(3)'-4(2)(-7) 

_2(2) 
-3± V&5 

4 
-3± ^65 



Step 4 : Write the final answer 

The two roots of f(x) = 2x 2 + 3x - 7 are x = - :i +/^> and ~ 3 ~^ . 



(7.11) 
(7.12) 
(7.13) 



Example 7: Using the quadratic formula but no solution 



QUESTION 



Find the solutions to the quadratic equation x 2 — 5x + 8 = 0. 



58 



CHAPTER 7. SOLVING QUADRATIC EQUATIONS 7.4 



SOLUTION 



Step 7 : Determine whether the equation can be factorised 

The expression cannot be factorised. Therefore, the general quadratic formula 
must be used. 



Step 2 : Identify the coefficients in the equation for use in the formula 

From the equation: 

o= 1 

6 =-5 

c = 8 



Step 3 : Apply the quadratic formula 

-b±Vb 2 -4ac 

X ~ 2a 



-(-5)±y/(-5P-4(l)(8) 
2(1) 



(7.14) 

(7.15) 

(7.16) 
(7.17) 



Step 4 : Write the final answer 

Since the expression under the square root is negative these are not real solutions 
(\/~^T is not a real number). Therefore there are no real solutions to the quadratic 
equation x 2 — 5x + 8 = 0. This means that the graph of the quadratic function 
f(x) = x 2 — 5x + 8 has no x-intercepts, but that the entire graph lies above the 
x-axis. 



See video: VMezc at www.everythingmaths.co.za 



Exercise 7 - 3 



Solve for t using the quadratic formula. 

1 . 3i 2 + t - 4 = 

2. t 2 -5t + 9 = 

3. 2t 2 + 6i + 5 = 

4. it 2 + 2t + 2 = 

5. -3t 2 + 54-8 = 

6. -5< 2 + 3* - 3 = 

7. t 2 - it + 2 = 



59 



7.4 



CHAPTER 7. SOLVING QUADRATIC EQUATIONS 



Tip 



In all the ex- 
amples done so 
far, the solutions 
were left in surd 
form. Answers 
can also be 
given in decimal 
form, using the 
calculator. Read 
the instructions 
when answering 
questions in a test 
or exam whether 
to leave answers 
in surd form, or 
in decimal form 
to an appropri- 
ate number of 
decimal places. 

Completing 
the square as a 
method to solve 
a quadratic equa- 
tion is only done 
when specifically 
asked. 



8. 9r - ft - 9 = 

9. 2i 2 + 3t + 2 = 
10. t 2 + t + l = 



(A 4 ) More practice (►) video solutions (9) or help at www.everythingmaths 



(1.)0190 (2.) 0191 (3.) 0192 (4.) 0193 (5.) 0194 (6.) 0195 
(7.) 0196 (8.) 0197 (9.) 0198 (10.) 0199 



Exercise 7-4 



Solve the quadratic equations by either factorisation, completing the square or by using the quadratic 
formula: 

• Always try to factorise first, then use the formula if the trinomial cannot be factorised. 

• Do some of them by completing the square and then compare answers to those done using the 
other methods. 



1. 24y 2 + 61y - 8 = 

2. -8j/ 2 - 16y + 42 = 

3. -9j/ 2 + 24y - 12 = 

4. -5j/ 2 + Qy + 5 = 

5. -3y 2 + 15y - 12 = 

6. 49j/ 2 + 0y - 25 = 

7. -12y 2 + my - 72 = 

8. — 40y 2 + 58y - 12 = 

9. -24y 2 + 37?/ + 72 = 

10. 6j/ 2 + 7y -24 = 

11. 2j/ 2 -5y-3 = 

12. -18y 2 -55j/-25 = 



13. -25j/ 2 + 25y - 4 = 

14. -32j/ 2 + 24y + 8 = 

15. 9y 2 -13y- 10 = 

16. 35j/ 2 -8y-3 = 

17. -81j/ 2 -99y- 18 = 

18. Uy 2 -Sly + 81 = 

19. -4j/ 2 -41s/ -45 = 

20. 16j/ 2 + 20j/ - 36 = 

21. 42j/ 2 + 104y + 64 = 

22. 9y 2 - 76y + 32 = 

23. -54j/ 2 + 21y + 3 = 

24. 36j/ 2 + 44j/ + 8 = 



25. 64i/ 2 + 96y + 36 = 

26. 12j/ 2 - 22y - 14 = 

27. 16j/ 2 + Oy - 81 = 

28. 3y 2 + lOy - 48 = 

29. -4j/ 2 + 8y - 3 = 

30. -5j/ 2 - 26j/ + 63 = 

31. x 2 -70 = 11 

32. 2a; 2 - 30 = 2 

33. x 2 - 16 = 2 - x 2 

34. 2j/ 2 - 98 = 

35. 5j/ 2 - 10 = 115 

36. 5j/ 2 - 5 = 19 - j/ 2 



A" 1 ) More practice \w) video solutions T9) or help at www.everythingmaths.co.za 



(1.)01zs (2.) 01 zt (3.)01zu (4.)01zv (5.) 01zw (6.) 01zx 

(7.)01zy (8.)01zz (9.) 0200 (10.) 0201 (11.) 0202 (12.) 0203 

(13.) 0204 (14.) 0205 (15.) 0206 (16.) 0207 (17.) 0208 (18.) 0209 

(19.) 020a (20.) 020b (21.) 020c (22.) 020d (23.) 020e (24.) 020f 

(25.) 020g (26.) 020h (27.) 020i (28.) 020j (29.) 020k (30.) 020m 

(31.)020n (32.) 020p (33.) 020q (34.) 020r (35.) 020s (36.) 020t 



(in 




CHAPTER 7. SOLVING QUADRATIC EQUATIONS 7.5 



7.5 Finding an Equation When You mEMBAJ 
Know its Roots 




We have mentioned before that the roots of a quadratic equation are the solutions or answers you get 
from solving the quadratic equation. Working back from the answers, will take you to an equation. 



Example 8: Find an equation when roots are given 



QUESTION 


Find an equation with roots 13 


and -5 






SOLUTION 








Step 1 : Write down as the product of two brackets 






The step before g 


ving the solutions would be: 
(x- 13)(x + 5) =0 






Notice that the sig 


ns in the brackets are opposite of the 


given roots. 




Step 2 : Remove brackets 


x 2 - 8x - 65 = 






Of course, there would be other possibilities as well 


when each term 


on each 


side of the equals 


sign is multiplied by a constant. 









Example 9: Fraction roots 



QUESTION 

Find an equation with roots — § and 4 

SOLUTION 



(il 



7.5 CHAPTER 7. SOLVING QUADRATIC EQUATIONS 



Step I : Product of two brackets 

Notice that if x = — § then 2x + 3 = 
Therefore the two brackets will be: 



Step 2 : Remove brackets 

The equation is: 



(2a: + 3) (a; -4) = 



2x 2 - 5x - 12 = 



Extension: 



Theory of Quadratic Equations - Advanced 



This section is not in the syllabus, but it gives one a good understanding about some of the 
solutions of the quadratic equations. 



What is the Discriminant of a Quadratic __ CkJOA „ 

._ ,. ~ ^ ■ EMBAK 

Equation? 

Consider a general quadratic function of the form f(x) = ax 2 + bx + c. The discriminant is 
defined as: 

A = 6 2 -4ac. (7.18) 

This is the expression under the square root in the formula for the roots of this function. We 
have already seen that whether the roots exist or not depends on whether this factor A is 
negative or positive. 



The Nature of the Roots W embal 



Real Roots (A > 0) 

Consider A > for some quadratic function f(x) = ax 2 + bx + c. In this case there are 
solutions to the equation f(x) = given by the formula 

-b ± s/W- - 4ac -b±VA 
X = 2a. = ^a— (7 - 19) 

If the expression under the square root is non-negative then the square root exists. These are 
the roots of the function f(x). 

There various possibilities are summarised in the figure below. 



(i2 



CHAPTER 7. SOLVING QUADRATIC EQUATIONS 



7.5 



A < : imaginary roots 



A > : real roots 

I 



A >0 
unequal roots 



A = 
equal roots 



A a per- 
fect square : 
rational roots 



A not a perfect 
square : irra- 
tional roots 



Equal Roots (A = 0) 

If A = 0, then the roots are equal and, from the formula, these are given by 

b 

X = — 7T- 

2a 



(7.20) 



Unequal Roots (A > 0) 

There will be two unequal roots if A > 0. The roots of f(x) are rational if A is a perfect 
square (a number which is the square of a rational number), since, in this case, \/A is rational. 
Otherwise, if A is not a perfect square, then the roots are irrational. 

Imaginary Roots (A < 0) 

If A < 0, then the solution to f(x) = ax 2 + bx + c = contains the square root of a negative 
number and therefore there are no real solutions. We therefore say that the roots of f(x) are 
imaginary (the graph of the function f(x) does not intersect the x-axis). 



© See video: VMfba at www.everythingmaths.co.za 



Extension: 



Theory of Quadratics - advanced exercises 



Exercise 7-5 



1 . [IEB, Nov. 2001 , HG] Given: x 2 + bx - 2 + k(x 2 + 3x + 2) = 0, (fc ^ -1) 

(a) Show that the discriminant is given by: 

A = k 2 + 6bk + b 2 + 8 

(b) If 6 = 0, discuss the nature of the roots of the equation. 

(c) If b = 2, find the value(s) of k for which the roots are equal. 

2. [IEB, Nov. 2002, HG] Show that k 2 x 2 + 2 = kx - x 2 has non-real roots for all real values 
for k. 

3. [IEB, Nov. 2003, HG] The equation x 2 + V2x = 3kx 2 + 2 has real roots. 

(a) Find the largest integral value of k. 

(b) Find one rational value of k, for which the above equation has rational roots. 

4. [IEB, Nov. 2003, HG] In the quadratic equation px 2 + qx + r = 0, p, q and r are positive 
real numbers and form a geometric sequence. Discuss the nature of the roots. 



(>:>, 



7.5 CHAPTER 7. SOLVING QUADRATIC EQUATIONS 



5. [IEB, Nov. 2004, HG] Consider the equation: 

x 2 — 4 

k = where i^ | 

2x - 5 2 

(a) Find a value of k for which the roots are equal. 

(b) Find an integer k for which the roots of the equation will be rational and unequal. 

6. [IEB, Nov. 2005, HG] 

(a) Prove that the roots of the equation x 2 — (a + b)x + ab — p 2 = are real for all real 
values of a, b and p. 

(b) When will the roots of the equation be equal? 

7. [IEB, Nov. 2005, HG] If 6 and c can take on only the values 1; 2 or 3, determine all pairs 
(6; c) such that x 2 + bx + c = has real roots. 



A" 1 ) More practice (►) video solutions CfJ or ne 'P at www.everythingmaths.co.za 



(1.)019a (2.) 019b (3.) 019c (4.) 019d (5.) 019e (6.) 01 9f 
(7.)019g 



Chapter 7 



End of Chapter Exercises 



1. Solve: a; — x — 1 = (Give your answer correct to two decimal places.) 

2. Solve: 16(x + 1) = x 2 {x + 1) 

12 

3. Solve: y 2 + 3 H — = = 7 (Hint: Let y 2 + 3 = k and solve for k first and use the 

y 2 + 3 
answer to solve j/.) 

4. Solve for x: 2x 4 - 5x 2 - 12 = 

5. Solve for x: 

(a) x(x - 9) + 14 = 

(b) x 2 — x = 3 (Show your answer correct to one decimal place.) 

(c) x + 2 = — (correct to two decimal places) 

x 

X + 1 x — 1 

6. Solve for x in terms of p by completing the square: x 2 — px — 4 = 

7. The equation ax 2 + bx + c = has roots x = | and x = —4. Find one set of possible 
values for a, b and c. 

8. The two roots of the equation 4x 2 +px — 9 = differ by 5. Calculate the value of p. 

9. An equation of the form x 2 + bx + c = is written on the board. Saskia and Sven 
copy it down incorrectly. Saskia has a mistake in the constant term and obtains 
the solutions —4 and 2. Sven has a mistake in the coefficient of x and obtains the 
solutions 1 and —15. Determine the correct equation that was on the board. 

10. Bjorn stumbled across the following formula to solve the quadratic equation ax 2 + 
bx + c = in a foreign textbook. 

_ 2c 

-6 ± Vb 2 - 4ac 



(il 



CHAPTER 7. SOLVING QUADRATIC EQUATIONS 7.5 

(a) Use this formula to solve the equation: 

2x 2 + x - 3 = 

(b) Solve the equation again, using factorisation, to see if the formula works for this 
equation. 

(c) Trying to derive this formula to prove that it always works, Bjorn got stuck along 
the way. His attempt his shown below: 



ax 



bx + c = 



b c 
a-\ 1 — - = Divided by x 2 where x ^ 



x x^ 



— la = Rearranged 



x* x 
1 b a 

x z cx c 



Divided by c where c ^ 



1 b a „ . . a , ii. i 

— H = — Subtracted - from both sides 

X 1 cx c c 

1 6 

— + — + ■• 
x z cx 



Got stuck 



Complete his derivation. 



f/Vy More practice (►) video solutions (?) or help at www.everythingmaths.co.za 



(1.)0l9h (2.)019i (3.)019j (4.) 019k (5.) 019m (6.)019n 
(7.)019p (8.)019q (9.)019r (10.) 019s 



(M 



Solving Quadratic 
Inequalities 





8. 1 Introduction 




Now that you know how to solve quadratic equations, you are ready to move on to solving quadratic 
inequalities. As with linear inequalities (which were covered in Grade 10) your solutions will be 
intervals on the number line, rather than single numbers. 

® See introductory video: VMfdy at www.everythingmaths.co.za 




8.2 Quadratic Inequalities 




A quadratic inequality is an inequality in one of the following forms: 

ax + bx + c > 

ax + bx + c > 

ax + bx + c < 

ax + bx + c < 

Solving a quadratic inequality corresponds to working out in what region the graph of a quadratic 
function lies above or below the x-axis. 



Example 1: Quadratic Inequality 



QUESTION 



Solve the inequality Ax 2 — Ax + 1 < and interpret the solution graphically. 



SOLUTION 



Step 1 : Factorise the quadratic 

Let f(x) = Ax 2 — Ax + 1. Factorising this quadratic function gives f(x) 
(2* -I) 2 . 



Step 2 : Re-write the original equation with factors 



66 



CHAPTER 8. SOLVING QUADRATIC INEQUALITIES 8.2 



(2x - l) 2 < 



Step 3 : Solve the equation 

f(x) = only when x = \. 



Step 4 : Write the final answer 

This means that the graph of f(x) = 4x 2 — Ax + 1 touches the x-axis at x = \, 
but there are no regions where the graph is below the x-axis. 



Step 5 : Graphical interpretation of solution 

x=\ 

* — I 1 1 1 1 1 — ♦ — I 1 1 h 

-2-10 1 2 



Example 2: Solving Quadratic Inequalities 



QUESTION 



Find all the solutions to the inequality x 2 — 5x + 6 > 0. 



SOLUTION 



Step 1 : Factorise the quadratic 

The factors of x 2 — 5x + 6 are (x — 3)(x — 2). 

Step 2 : Write the inequality with the factors 

x — bx + 6 > 
(x-3)(x-2) > 

Step 3 : Determine which ranges correspond to the inequality 

We need to figure out which values of x satisfy the inequality. From the answers 
we have five regions to consider. 



A BCD E 
H • • 1- 



Step 4 : Determine whether the function is negative or positive in each of the regions 

Let f(x) = x 2 — bx + 6. For each region, choose any point in the region and 
evaluate the function. 



67 



8.2 CHAPTER 8. SOLVING QUADRATIC INEQUALITIES 







/(*) 


sign 


of/(x) 


Region A 


x < 2 


/(I) = 2 




+ 


Region B 


x = 2 


/(2) = 




+ 


Region C 


2 < x < 3 


/(2,5) = -2,5 




- 


Region D 


x = 3 


/(3) = 




+ 


Region E 


x > 3 


/(4) = 2 




+ 



We see that the function is positive for x < 2 and x > 3. 

Step 5 : Write the final answer and represent on a number line 

We see that x 2 - 5x + 6 > is true for x < 2 and x > 3. 

< I I 1 I ) 



Example 3: Solving Quadratic Inequalities 



QUESTION 



Solve the quadratic inequality —x 2 — 3x + 5 > 0. 



SOLUTION 



Step 1 : Determine how to approach the problem 

Let f(x) = —x 2 — 3x + 5. f(x) cannot be factorised so, use the quadratic 
formula to determine the roots of f{x). The z-intercepts are solutions to the 
quadratic equation 



— x — 3x + 5 


= 





x + 3x — 5 


= 







-3±V(3) 2 -4(l)(-5) 




2(1) 






-3± v/29 






2 


Xl 


= 


-3-^_ 4 , 2 


X2 


= 


-3 + ^29 

2 ~ M 



Step 2 : Determine which ranges correspond to the inequality 

We need to figure out which values of x satisfy the inequality. From the answers 
we have five regions to consider. 

A BCD E 
1 • • 1 ► 



-4,2 1,2 



68 



CHAPTER 8. SOLVING QUADRATIC INEQUALITIES 



8.2 



Step 3 : Determine whether the function is negative or positive in each of the regions 

We can use another method to determine the sign of the function over differ- 
ent regions, by drawing a rough sketch of the graph of the function. We know 
that the roots of the function correspond to the x-intercepts of the graph. Let 
g(x) = —x 2 — Sx + 5. We can see that this is a parabola with a maximum turning 
point that intersects the x-axis at —4,2 and 1,2. 

























\7 - 














V 














5 J 














4 - 














3 - 














2 - 














1 - 






Si 


/ 










,w 




-4 


-3 


-2 


-1 

-1 - 




1 \ ' 

l\ 



It is clear that g(x) > for xi < x < x 2 



Step 4 : Write the final answer and represent the solution graphically 

-x 2 - 3x + 5 > for -4,2 < x < 1,2 



-4,2 1,2 



When working with an inequality in which the variable is in the denominator, a different approach is 
needed. 



Example 4: Non-linear inequality with the variable in the denominator 



QUESTION 



Solve < 



x + 3 x — 3 



SOLUTION 



(il) 



8.2 CHAPTER 8. SOLVING QUADRATIC INEQUALITIES 



Step I : Subtract ^^ from both sides 

2 1 



<0 



x + 3 x — 3 
Step 2 : Simplify the fraction by finding LCD 



2(g-3)-(g + 3) <Q 



(x + 3)(x-3) 
x-9 



<0 



Step 3 : Draw a number line for the inequality 

— undef + undef — 

— i 1 r 

-3 3 9 

We see that the expression is negative for x < — 3 or 3 < x < 9. 

Step 4 : Write the final answer 

x < —3 or 3 < x < 9 



See video: VMfeu at www.everythingmaths.co.za 



Chapter 8 



End of Chapter Exercises 



Solve the following inequalities and show your answer on a number line: 

1. Solve: x 2 - x < 12. 

2. Solve: 3x 2 > -x + 4 

3. Solve: y 2 < -y - 2 

4. Solve: -t 2 + It > -3 

5. Solve: s 2 - 4s > -6 

6. Solve: > 7a; 2 - x + 8 

7. Solve: > -Ax 2 - x 

8. Solve: > 6x 2 

9. Solve: 2x 2 + x + 6 < 

10. Solve for x if: — ^— < 2 and x ^ 3. 

x — 3 

4 

1 1 . Solve for x if: < 1, 

x — 3 



70 



CHAPTER 8. SOLVING QUADRATIC INEQUALITIES 8.2 



4 

12. Solve for x if: — - < 1. 

(x — 3) 2 

2x — 2 

13. Solve for x: > 3 

x — 3 

14. Solve for x: — - — < 

(i--3)(x + l) 

15. Solve: (2a - 3) 2 < 4 

1 6. Solve: 2x < ^Z^ 

x 

1 7. Solve for x: < 

3x-2 ~ 

18. Solve: x - 2 > - 



19. Solve for x: x ' + 3x 4 < 

5 + x 4 

x — 2 

20. Determine all real solutions: > 1 

3 — x 



UP) More practice (►) video solutions fjM or help at www.everythingmaths.co.za 



(1.)019t (2.)019u (3.)019v (4.)019w (5.)019x (6.)019y 

(7.)019z (8.)01a0 (9.) 01a1 (10.) 01a2 (1 1.) 01 a3 (12.) 01a4 

(13.) 01a5 (14.) 01a6 (15.)01a7 (16.) 01a8 (17.)01a9 (18.) 01aa 

(19.)01ab (20.)01ac 



71 



Solving Simultaneous 
Equations 





9. 7 Introduction 




In Grade 10, you learnt how to solve sets of simultaneous equations where both equations were linear 
(i.e. had the highest power equal to 1). In this chapter, you will learn how to solve sets of simultaneous 
equations where one is linear and one is quadratic. As in Grade 10, the solution will be found both 
algebraically and graphically. 

The only difference between a system of linear simultaneous equations and a system of simultaneous 
equations with one linear and one quadratic equation, is that the second system will have at most two 
solutions. 

An example of a system of simultaneous equations with one linear equation and one quadratic equa- 
tion is: 



y — 2x = — 4 
x + y = 4 

® See introductory video: VMfwh at www.everythingmaths.co.za 



(9.1) 




9.2 Graphical Solution 




The method of graphically finding the solution to one linear and one quadratic equation is identical to 
systems of linear simultaneous equations. 



Method: Graphical solution to a system of 
simultaneous equations with one linear and 
one quadratic equation 



EMBAQ 



1 . Make y the subject of each equation. 

2. Draw the graphs of each equation as defined above. 

3. The solution of the set of simultaneous equations is given by the intersection points of the two 
graphs. 

For this example, making y the subject of each equation, gives: 

y = 2x - 4 

A 2 

y = 4 — x 

Plotting the graph of each equation, gives a straight line for the first equation and a parabola for the 
second equation. 



72 



CHAPTER 9. SOLVING SIMULTANEOUS EQUATIONS 



9.2 









l 1 1 


/ 2 - 


. \(2;0)/ 

ir 1 1 




1 1 1 

-6 -4 , 


^2_ 2 - 


A 1 1 
. / 2\ 4 6 




^ / 


-4 , 






III 


/ -8 - 








-10 - 






(-4;-12)jT 


-12 - 








-14 - 













The parabola and the straight line intersect at two points: (2;0)and (—4;— 12). Therefore, the solutions 
to the system of equations in (9.1) is a; = 2; y = and x = —4;y = 12 



Example 1: Simultaneous Equations 



QUESTION 



Solve graphically: 



y - x + 9 = 
y + 'Ax - 9 = 



SOLUTION 



Step 1 : Make y the subject of the equation 

For the first equation: 

y - x 1 + 9 = 



y = x — 9 



and for the second equation: 



y + Ax - 9 = 

y = -3x + 9 

Step 2 : Draw the graphs corresponding to each equation. 



7;>> 



9.3 



CHAPTER 9. SOLVING SIMULTANEOUS EQUATIONS 



(-6; 27) 



H 1 h 




-6 -4 \2 



6 8 



Step 3 : Find the intersection of the graphs. 

The graphs intersect at (-6; 27) and at (3; 0). 

Step 4 : Write the solution of the system of simultaneous equations as given by the 
intersection of the graphs. 

The first solution is x = — 6 and y = 27. The second solution is x = 3 and y = 0. 



Exercise 9-1 



Solve the following systems of equations graphically. Leave your answer in surd form, where appropri- 
ate. 

1. 6 2 -l-a = 0;a + fe-5 = 

2. x + y -10 = 0;x 2 -2-y = 

3. 6 - Ax - y = 0; 12 - 2x 2 - y = 

4. x + 2y - 14 = 0; x 1 + 2 - y = 

5. 2x + 1 - y = 0; 25 - 3z - x 2 - y = 

(ft" 1 ) More practice (►) video solutions (9) or help at www.everythingmaths.co.za 
(1.)01ad (2.)01ae (3.) 01af (4.) 01ag (5.) 01 ah 




9.3 Algebraic Solution 




The algebraic method of solving simultaneous equations is by substitution. 



71 



CHAPTER 9. SOLVING SIMULTANEOUS EQUATIONS 9.3 



For example the solution of 



y-2x = -4 (9.2) 

x 2 + y = 4 (9.3) 



In (9.2) 



Substitute (9.4) into (9.3): 



Facto rise to get: 



y = 2x-4 (9.4) 



x + (2x - 4) = 4 
x 2 + 2x - 8 = 



(x + 4)(x-2) = 

.-. x = — 4 and x = 2 

Substitute the values of x into (9.4) to find y: 

j/ = 2(-4)-4 2/ = 2(2) -4 

3/ = -12 y = 

(-4; -12) (2:0) 

As expected, these solutions are identical to those obtained by the graphical solution. 



Example 2: Simultaneous Equations 



QUESTION 

Solve algebraically: 



y-x-' + Q = (9.5) 

2/ + 3x-9 = (9.6) 



SOLUTION 



Step 1 : Make y the subject of the linear equation 

In (9.5): 



y + 3x - 9 = 

y = -3x + 9 (9.7) 



Step 2 : Substitute into the quadratic equation 



75 



9.3 



CHAPTER 9. SOLVING SIMULTANEOUS EQUATIONS 



Substitute (9.7) into (9.5): 



Facto rise to get: 



(-3x + 9) - x 2 + 9 = 
x 2 + 3x - 18 = 



(x + 6)(x-3) = 

.'. x = —6 and x = 3 



Step 3 : Substitute the values for x into the first equation to calculate the corresponding 
y-values. 

Substitute x into 9.5: 



j/ = -3(-6)+9 

= 27 
(-6; 27) 



y = -3(3) +9 
= 
(3;0) 



Step 4 : Write the solution of the system of simultaneous equations. 

The first solution is x = -6 and y = 27. The second solution is x = 3 and y = 0. 



Chapter 9 



End of Chapter Exercises 



Solve the following systems of equations algebraically. Leave your answer in surd form, 
where appropriate. 

1 . a + 6 = 5;a-6 2 + 36-5 = 

2. a-6+l = 0;a-6 2 + 56-6 = 



3. a - 

4. a- 

5. a - 

6. a 

7. a 



(2b+2) 



a - 26 2 + 36 + 5 = 
26 - 4 = ; a - 26 2 - 56 + 3 = 
2 + 36 = 0;a-9 + 6 2 =0 
6-5 = 0;a-6 2 =0 
6-4 = 0;a + 26 2 -12 = 

8. a + 6-9 = 0;a + 6 2 -18 = 

9. a-36 + 5 = 0;a + 6 2 -46 = 

10. a + 6-5 = 0;a-6 2 + l = 

11. a- 26 -3 = 0; a-36 2 +4 = 

12. a-26 = 0;a-6 2 -26 + 3 = 

13. a- 36 = 0; a- 6 2 +4 = 

14. a - 26 - 10 = ; a - 6 2 - 56 = 

15. a - 36 - 1 = ; a - 26 2 - 6 + 3 = 

16. a-36+1 = 0; a-6 2 = 

17. a + 66-5 = 0;a-6 2 -8 = 



7(i 



CHAPTER 9. SOLVING SIMULTANEOUS EQUATIONS 9.3 

18. a - 26 + 1 = ; a - 2b 2 - 126 + 4 = 

19. 2q + 6 - 2 = ; 8a + 6 2 - 8 = 

20. a + 46 - 19 = ; 8a + 56 2 - 101 = 

21. a + 46 - 18 = ; 2a + 56 2 - 57 = 

f/Vj More practice CrJ video solutions (9) or help at www.everythingmaths.co.za 

(l.)020u (2.) 020v (3.) 020w (4.) 020x (5.) 020y (6.) 020z 

(7.) 0210 (8.) 0211 (9.) 0212 (10.) 0213 (11.) 0214 (12.) 0215 

(13.) 0216 (14.) 0217 (15.) 0218 (16.) 0219 (17.) 021a (18.) 021b 

(19.) 021c (20.) 021 d (21.)021e 



77 



Mathematical Models 





10.1 Introduction 



EMBAS 



Up until now, you have only learnt how to solve equations and inequalities, but there has not been 
much application of what you have learnt. This chapter builds on this knowledge and introduces you 
to the idea of a mathematical model, which uses mathematical concepts to solve real-world problems. 

© See introductory video: VMfjh at www.everythingmaths.co.za 




10.2 Mathematical Models 



EMBAT 



DEFINITION: Mathematical Model 

A mathematical model is a method of using the mathematical language to describe 
the behaviour of a physical system. Mathematical models are used particularly in the 
natural sciences and engineering disciplines (such as physics, biology, and electrical 
engineering) but also in the social sciences (such as economics, sociology and political 
science); physicists, engineers, computer scientists, and economists use mathematical 
models most extensively. 



A mathematical model is an equation (or a set of equations for the more difficult problems) that de- 
scribes a particular situation. For example, if Anna receives R3 for each time she helps her mother 
wash the dishes and R5 for each time she helps her father cut the grass, how much money will Anna 
earn if she helps her mother to wash the dishes five times and helps her father to wash the car twice? 
The first step to modelling is to write the equation, that describes the situation. To calculate how much 
Anna will earn we see that she will earn : 



5 x R3 for washing the dishes 

+ 2 x R5 for cutting the grass 

= R15 + RIO 
= R25 



If however, we ask: "What is the equation if Anna helps her mother x times and her father y times?" 
then we have: 



Total earned = (x x R3) + (jx R5) 



78 



CHAPTER 10. MATHEMATICAL MODELS 



10.3 




10.3 Real-World Applications 



Some examples of where mathematical models are used in the real-world are: 



1. To model population growth 

2. To model effects of air pollution 

3. To model effects of global warming 

4. In computer games 

5. In the sciences (e.g. physics, chemistry, biology) to understand how the natural world works 

6. In simulators that are used to train people in certain jobs, like pilots, doctors and soldiers 

7. In medicine to track the progress of a disease 



Activity: 



Simple Models 



In order to get used to the idea of mathematical models, try the following simple models. 
Write an equation that describes the following real-world situations, mathematically: 

1. Jack and Jill both have colds. Jack sneezes twice for each sneeze of Jill's. If Jill sneezes x 
times, write an equation describing how many times they both sneezed? 

2. It rains half as much in July as it does in December. If it rains y mm in July, write an 
expression relating the rainfall in July and December. 

3. Zane can paint a room in 4 hours. Billy can paint a room in 2 hours. How long will it 
take both of them to paint a room together? 

4. 25 years ago, Arthur was 5 more than | as old as Lee was. Today, Lee is 26 less than 
twice Arthur's age. How old is Lee? 

5. Kevin has played a few games of ten-pin bowling. In the third game, Kevin scored 80 
more than in the second game. In the first game Kevin scored 110 less than the third 
game. His total score for the first two games was 208. If he wants an average score of 
146, what must he score on the fourth game? 

6. Erica has decided to treat her friends to coffee at the Corner Coffee House. Erica paid 
R54,00 for four cups of cappuccino and three cups of filter coffee. If a cup of cappuccino 
costs R3,00 more than a cup of filter coffee, calculate how much each type of coffee 
costs? 

7. The product of two integers is 95. Find the integers if their total is 24. 



79 



10.3 CHAPTER 10. MATHEMATICAL MODELS 



Example 1: Mathematical Modelling of Falling Objects 



QUESTION 



When an object is dropped or thrown downward, the distance, d, that it falls in time, t is 
described by the following equation: 

s = 5i + vot 

In this equation, v is the initial velocity, in m • s _1 . Distance is measured in meters and time 
is measured in seconds. Use the equation to find how far an object will fall in 2 s if it is 
thrown downward at an initial velocity of 10 m • s _1 . 



SOLUTION 



Step 1 : Identify what is given for each problem 

We are given an expression to calculate distance travelled by a falling object in 
terms of initial velocity and time. We are also given the initial velocity and time 
and are required to calculate the distance travelled. 



Step 2 : List all known and unknown information 

• vo = 10 m ■ s _1 

• t = 2 s 



Step 3 : Substitute values into expression 

s = 5t + vot 

= 5(2) 2 + (10)(2) 

= 5(4) + 20 

= 20 + 20 

= 40 



Step 4 : Write the final answer 

The object will fall 40 m in 2 s if it is thrown downward at an initial velocity of 
10 m-s" 1 . 



80 



CHAPTER 10. MATHEMATICAL MODELS 



10.3 



Example 2: Another Mathematical Modelling of Falling Objects 



QUESTION 



When an object is dropped or thrown downward, the distance, d, that it falls in time, t is 
described by the following equation: 

s = 54 + vot 

In this equation, v is the initial velocity, in m • s _1 . Distance is measured in meters and time 
is measured in seconds. Use the equation find how long it takes for the object to reach the 
ground if it is dropped from a height of 2000 m. The initial velocity is m • s~ x . 



SOLUTION 



Step 1 



: Identify what is given for each problem 

We are given an expression to calculate distance travelled by a falling object 
in terms of initial velocity and time. We are also given the initial velocity and 
distance travelled and are required to calculate the time it takes the object to 
travel the distance. 



Step 2 : List all known and unknown information 

• Vo = m ■ s _1 

• t =?s 

• s = 2000 m 

Step 3 : Substitute values into expression 



s 


= 


5t + vot 


2000 


= 


5t 2 + (0)(2) 


2000 


= 


5t 2 


t 2 


= 


2000 
5 




= 


400 


', t 


= 


20 s 



Step 4 : Write the final answer 

The object will take 20 s to reach the ground if it is dropped from a height of 
2 000 m. 



Activity: 






Mathematical Modelling 



The graph below shows how the distance travelled by a car depends on time. Use the 
graph to answer the following questions. 



.si 



10.3 



CHAPTER 10. MATHEMATICAL MODELS 



400 -- 



■§ 300 4 




200 -- 



100 -- 



20 30 40 
Time (s) 

1 . How far does the car travel in 20 s? 

2. How long does it take the car to travel 300 m? 



Example 3: More Mathematical Modelling 



QUESTION 



A researcher is investigating the number of trees in a forest over a period of n years. After 
investigating numerous data, the following data model emerged: 



Year 


Number of trees (in hundreds) 


1 


1 


2 


3 


3 


9 


4 


27 



7. How many trees, in hundreds, are there in the sixth year if this pattern is continued? 

2. Determine an algebraic expression that describes the number of trees in the n th year in 
the forest. 

3. Do you think this model, which determines the number of trees in the forest, will con- 
tinue indefinitely? Give a reason for your answer. 



SOLUTION 



Step 1 : Find the pattern 

The pattern is 3° ; 3 1 ; 3 2 ; 3 3 ; . . . 

Therefore, three to the power one less than the year. 

Step 2 : Trees in year 6 

Year 6 : 3 5 hundred = 243 hundred = 24300 
Step 3 : Algebraic expression for year n 

Number of trees = 3" _1 hundred 



<N2 



CHAPTER 10. MATHEMATICAL MODELS 



10.3 



Step 4 : Conclusion 

No, the number of trees will not increase indefinitely. The number of trees will 
increase for some time. Yet, eventually the number of trees will not increase 
any more. It will be limited by factors such as the limited amount of water and 
nutrients available in the ecosystem. 



Example 4: Setting up an equation 



QUESTION 



Currently the subscription to a gym for a single member is Rl 000 annually while family 
membership is Rl 500. The gym is considering raising all memberships fees by the same 
amount. If this is done then the single membership will cost | of the family membership. 
Determine the proposed increase. 



SOLUTION 



Step 1 : Summarise the information in a table 

Let the proposed increase be x. 





Now 


After increase 


Single 


1000 


1 000 + x 


Family 


1500 


1 500 + x 



Step 2 : Set up an equation 



1000 



+ x = -(1 500 + x) 



Step 3 : Solve the equation. 



7 000 + 7x 
2x 



7 500 + 5x 

500 

250 



Step 4 : Write down the answer 

Therefore the increase is R250. 



83 



10.3 



CHAPTER 10. MATHEMATICAL MODELS 



Extension: 



Simulations 



A simulation is an attempt to model a real-life situation on a computer so that it can be stud- 
ied to see how the system works. By changing variables, predictions may be made about the 
behaviour of the system. Simulation is used in many contexts, including the modelling of nat- 
ural systems or human systems in order to gain insight into their functioning. Other contexts 
include simulation of technology for performance optimisation, safety engineering, testing, 
training and education. Simulation can be used to show the eventual real effects of alternative 
conditions and courses of action. 

Simulation in education Simulations in education are somewhat like training simulations. They 
focus on specific tasks. In the past, video has been used for teachers and education students to 
observe, problem solve and role play; however, a more recent use of simulations in education 
is that of animated narrative vignettes (ANV). ANVs are cartoon-like video narratives of hypo- 
thetical and reality-based stories involving classroom teaching and learning. ANVs have been 
used to assess knowledge, problem solving skills and dispositions of children and pre-service 
and in-service teachers. 



Chapter 1 



End of Chapter Exercises 



When an object is dropped or thrown downward, the distance, d, that it falls in time, 
t, is described by the following equation: 



5r 



-v t 



In this equation, v a is the initial velocity, in m ■ s _1 . Distance is measured in meters 
and time is measured in seconds. Use the equation to find how long it takes a tennis 
ball to reach the ground if it is thrown downward from a hot-air balloon that is 500 m 
high. The tennis ball is thrown at an initial velocity of 5 m ■ s _1 . 

2. The table below lists the times that Sheila takes to walk the given distances. 



Time (minutes) 


5 


10 


15 


20 


25 


30 


Distance (km) 


1 


2 


3 


4 


5 


6 



Plot the points. 

If the relationship between the distances and times is linear, find the equation of the 

straight line, using any two points. Then use the equation to answer the following 

questions: 

(a) How long will it take Sheila to walk 21 km? 

(b) How far will Sheila walk in 7 minutes? 

If Sheila were to walk half as fast as she is currently walking, what would the graph 
of her distances and times look like? 

3. The power P (in watts) supplied to a circuit by a 12 volt battery is given by the 
formula P = 121 — 0,5/ 2 where I is the current in amperes. 

(a) Since both power and current must be greater than 0, find the limits of the current 
that can be drawn by the circuit. 

(b) Draw a graph of P = 121 — 0,5/ 2 and use your answer to the first question, to 
define the extent of the graph. 

(c) What is the maximum current that can be drawn? 



81 



CHAPTER 10. MATHEMATICAL MODELS 



10.3 



(d) From your graph, read off how much power is supplied to the circuit when the 
current is 10 Amperes. Use the equation to confirm your answer. 

(e) At what value of current will the power supplied be a maximum? 

You are in the lobby of a business building waiting for the lift. You are late for a 
meeting and wonder if it will be quicker to take the stairs. There is a fascinating 
relationship between the number of floors in the building, the number of people in 
the lift and how often it will stop: 

If N people get into a lift at the lobby and the number of floors in the 
building is F, then the lift can be expected to stop 



F - 



F - 



times. 

(a) If the building has 16 floors and there are 9 people who get into the lift, how 
many times is the lift expected to stop? 

(b) How many people would you expect in a lift, if it stopped 12 times and there are 
17 floors? 

5. A wooden block is made as shown in the diagram. The ends are right-angled triangles 
having sides 3x, Ax and 5x. The length of the block is y. The total surface area of the 
block is 3600 cm 2 . 




Show that 



300 - x 2 



6. A stone is thrown vertically upwards and its height (in metres) above the ground at 
time t (in seconds) is given by: 

h(t) = 35 - 5< 2 + 30i 



Find its initial height above the ground. 

7. After doing some research, a transport company has determined that the rate at which 
petrol is consumed by one of its large carriers, travelling at an average speed of x km 
per hour, is given by: 

P(x) = 1 litres per kilometre 

K ' 2x 200 H 

Assume that the petrol costs R4,00 per litre and the driver earns R18,00 per hour 



85 



10.3 



CHAPTER 10. MATHEMATICAL MODELS 



(travelling time). Now deduce that the total cost, C, in Rands, for a 2 000 km trip is 
given by: 

_, , 256000 „„ 

C{x) = + 40x 



8. During an experiment the temperature T (in degrees Celsius), varies with time t (in 
hours), according to the formula: 

T(t) =30 + At- it 2 te[l;10] 

(a) Determine an expression for the rate of change of temperature with time. 

(b) During which time interval was the temperature dropping? 

9. In order to reduce the temperature in a room from 28° C, a cooling system is allowed 
to operate for 10 minutes. The room temperature, T after t minutes is given in ° C 
by the formula: 

T = 28 - 0,008i 3 - 0,16i where t £ [0; 10] 

(a) At what rate (rounded off to two decimal places) is the temperature falling when 
t = A minutes? 

(b) Find the lowest room temperature reached during the 10 minutes for which the 
cooling system operates, by drawing a graph. 

10. A washing powder box has the shape of a rectangular prism as shown in the diagram 
below. The box has a volume of 480 cm 3 , a breadth of 4 cm and a length of x cm. 



Washing powder 



Show that the total surface area of the box (in cm 2 ) is given by: 
A = 8x + 960x _1 +240 



Q\+) More practice (►) video solutions CfJ or help at www.everythingmaths.co.za 



(l.)010w (2.)010x (3.)010y (4.) OIOz (5.) 0110 (6.) 0111 
(7.) 0112 (8.) 0113 (9.) 0114 (10.) 0115 



.N(> 



Quadratic Functions and 
Graphs 





11.1 Introduction 




In Grade 10, you studied graphs of many different forms. Here you will learn how to sketch and 
interpret more general quadratic functions. 

© See introductory video: VMfkg at www.everythingmaths.co.za 




7 7.2 Functions of the Form 

y = a(x +p) 2 + q 



This form of the quadratic function is slightly more complex than the form studied in Grade 10, y = 
ax 2 + q. The general shape and position of the graph of the function of the form fix) = a(x + p) 2 + q 
is shown in Table 11.1. 




-3 -■- 
Figure 11.1: Graph of f(x) = \{x + 2) 2 - 1 



Activity: 



Functions of the Form y — a(x + p) 2 + q 



1 . On the same set of axes, plot the following graphs: 

(a) a(x) = {x- 2) 2 

(b) b(x) = (x- l) 2 

(c) c(x) = x 2 



87 



11.2 



CHAPTER 



QUADRATIC FUNCTIONS AND GRAPHS 



(d) d(x) = (x + l) 2 

(e) e(x) = (x + 2) 2 

Use your results to deduce the effect of p. 

2. On the same set of axes, plot the following graphs: 

(a) f{x) = {x-2) 2 + l 

(b) g(x) = {x-l) 2 + l 

(c) h(x) = x 2 + 1 

(d) ]{x) = (x + l) 2 + l 

(e) k(x) = (x + 2) 2 + 1 

Use your results to deduce the effect of q. 

3. Following the general method of the above activities, choose your own values of p and 
q to plot 5 different graphs (on the same set of axes) of y = a(x + p) 2 + q to deduce the 
effect of a. 



From your graphs, you should have found that a affects whether the graph makes a smile or a frown. If 
a < 0, the graph makes a frown and if a > then the graph makes a smile. This was shown in Grade 
10. 

You should have also found that the value of q affects whether the turning point of the graph is above 
the x-axis (q < 0) or below the x-axis (q > 0). 

You should have also found that the value of p affects whether the turning point is to the left of the 
2/-axis (p > 0) or to the right of the j/-axis (p < 0). 

These different properties are summarised in Table 11.1. The axes of symmetry for each graph is shown 
as a dashed line. 



Table 11.1: Table summarising general shapes and positions of functions of the form y = a(x+p) 2 + q. 
The axes of symmetry are shown as dashed lines. 





p< 


p>o 




a > 


a < 


a > 


a < 


q> 


* 


I / 




■ I 
I 




t 


I 
I 




' 


I 

I 
I 




/ 


I \ 
I 


I 

I 
I 




/ ! 
i 
i 


\ 


q < 


. \ 


I 
I 
I t 


. 


I 
I 


I 
I 


t , 


i 
i 
i 




1 


I 

I 




t 


nV 


I 
I 




'/ij 


\ 



See simulation: VMflm at www.everythingmaths.co.za) 



Domain and Range 



EMBAX 



For f(x) = a(x + p) 2 + q, the domain is {x : x e M} because there is no value of x e E for which 
f(x) is undefined. 



88 



CHAPTER 11. QUADRATIC FUNCTIONS AND GRAPHS 11.2 



The range of f(x) = a(x+p) 2 + q depends on whether the value for a is positive or negative. We will 
consider these two cases separately. 

If a > then we have: 

(x + p) 2 > (The square of an expression is always positive) 

a(x + p) 2 > (Multiplication by a positive number maintains the nature of the inequality) 

a(x +p) + q > q 

fix) > q 

This tells us that for all values of x, f(x) is always greater than or equal to q. Therefore if a > 0, the 
range of f(x) = a(x + p) 2 + q is {/(or) : f(x) G [q,oo)}. 

Similarly, it can be shown that if a < that the range of f(x) = a(x+p) 2 +q is {f(x) : f(x) G (— oo,ij]}. 
This is left as an exercise. 

For example, the domain of g{x) = (x — l) 2 + 2 is {x : x e R} because there is no value of x e M. for 
which g(x) is undefined. The range of g(x) can be calculated as follows: 



(x-p) > 

2 + 2 > 2 
g(x) > 2 



(x+p) 2 + 2 > 2 



Therefore the range is {g{x) : g(x) e [2,oo)}. 



Exercise 11-1 



1 . Given the function f(x) = (x — 4) 2 — 1. Give the range of f{x). 

2. What is the domain of the equation y = 2x 2 — 5x — 18? 

Q\+) More practice (►) video solutions Cfj or help at www.everythingmaths.co.za 
(1.) 0116 (2.) 0117 

In tercepts V emba y 



For functions of the form, y = a(x + p) 2 + q, the details of calculating the intercepts with the x and y 
axes is given. 

The y-intercept is calculated as follows: 



y = a(x + pY + q (11.1) 

Vint = a(0 + p) 2 +q (11.2) 

= ap 2 + q (11 .3) 

Ifp = 0, then y int = q. 

89 



11.2 CHAPTER 11. QUADRATIC FUNCTIONS AND GRAPHS 

For example, the j/-intercept of g(x) = (x - l) 2 + 2 is given by setting x = to get: 

<?0r) = (x-l) 2 +2 
Vint = (0 - l) 2 + 2 
= (-l) 2 +2 
= 1 + 2 
= 3 

The x-intercepts are calculated as follows: 

y = a{x+pf+q (11.4) 

= a(xint +pf + q (11.5) 

a{x int +pf = -q (11.6) 

Xint+P = ±a/-^ (11-7) 

s int = ±J---p (11.8) 



a 

However, (1 1.8) is only valid if — f > which means that either q < or a < but not both. This 
is consistent with what we expect, since if q > and a > then — f is negative and in this case the 
graph lies above the x-axis and therefore does not intersect the a;-axis. If however, q > and a < 0, 
then — 2 is positive and the graph is hat shaped with turning point above the x-axis and should have 
two x-intercepts. Similarly, if q < and a > then — f is also positive, and the graph should intersect 
with the x-axis twice. 

For example, the x-intercepts of g(x) = (x — l) 2 + 2 are given by setting y = to get: 

g{x) = (x-l) 2 + 2 

= (X int - l) 2 + 2 

-2 = (x int - 1) 
which has no real solutions. Therefore, the graph of g(x) = (x — l) 2 + 2 does not have any x-intercepts. 



Exercise 11-2 



1 . Find the x- and y-intercepts of the function /(x) = (x — 4) 2 — 1. 

2. Find the intercepts with both axes of the graph of /(x) = x 2 — 6x + 8. 

3. Given: /(x) = — x 2 + 4x — 3. Calculate the x- and y-intercepts of the graph of /. 

A"y More practice (►) video solutions f9 ) or help at www.everythingmaths.co.za 
(1.) 01 18 (2.) 0119 (3.) 011a 



Turning Points mEMBAz 



The turning point of the function of the form /(x) = a(x + p) 2 + q is given by examining the range of 
the function. We know that if a > then the range of /(x) = a(x + p) 2 + q is {/(x) : /(x) e [<?,oo)} 
and if a < then the range of /(x) = a(x + p) 2 + q is {/(x) : /(x) G (— oo,g]}. 

90 



CHAPTER 11. QUADRATIC FUNCTIONS AND GRAPHS 11.2 



So, if a > 0, then the lowest value that f(x) can take on is q. Solving for the value of x at which 
f(x) = q gives: 

q = a(x + p) +q 

= a(x + p) 

= (x+pf 

= x + p 

x = — p 

:. x = — p at f(x) = q. The co-ordinates of the (minimal) turning point are therefore (— p; q). 

Similarly, if a < 0, then the highest value that f(x) can take on is q and the co-ordinates of the 
(maximal) turning point are (— p; q). 



Exercise 11 -3 



1 . Determine the turning point of the graph of f(x) = x 2 — Gx + 8. 

2. Given: f(x) = —x 2 + Ax — 3. Calculate the co-ordinates of the turning point of /. 

3. Find the turning point of the following function: 

j/=i(x + 2) 2 -l. 



Q\n More practice f ►) video solutions (9) or help at www.everythingmaths.co.za 



(1.) 01 lb (2.) 011c (3.) 01 Id 



Axes of Symmetry W embba 



There is only one axis of symmetry for the function of the form f(x) = a(x +p) 2 + q. This axis passes 
through the turning point and is parallel to the j/-axis. Since the x-coordinate of the turning point is 
x = — p, this is the axis of symmetry. 



Exercise 11 -4 



1 . Find the equation of the axis of symmetry of the graph y = 2x 2 — 5x — 18. 

2. Write down the equation of the axis of symmetry of the graph of 

y = 3(x - 2) 2 + 1. 

3. Write down an example of an equation of a parabola where the j/-axis is the axis of symmetry. 



Q\n More practice (►) video solutions f9) or help at www.everythingmaths 



(1.)011e (2.) 01 If (3.) 011g 



91 



11.2 CHAPTER 11. QUADRATIC FUNCTIONS AND GRAPHS 

Sketching Graphs of the Form fix) = a(x + 
p) +q 

In order to sketch graphs of the form f(x) = a(x + p) 2 + q, we need to determine five characteristics: 

1 . sign of a 

2. domain and range 

3. turning point 

4. ^/-intercept 

5. z-intercept (if appropriate) 

For example, sketch the graph of g(x) = — \{x + l) 2 — 3. Mark the intercepts, turning point and axis 
of symmetry. 

Firstly, we determine that a < 0. This means that the graph will have a maximal turning point. 

The domain of the graph is {x : x e M} because f(x) is defined for all x 6 R. The range of the graph 
is determined as follows: 

O + i) 2 > o 

-\{x + l) 2 < 
-\{x + l) 2 -'i < -3 

Therefore the range of the graph is {/(x) : f(x) e (— oo, — 3]}. 

Using the fact that the maximum value that f(x) achieves is —3, then the y-coordinate of the turning 
point is —3. The x-coordinate is determined as follows: 

- l -(x + l) 2 -Z = -3 

-i(x + l) 2 -3 + 3 = 

-\{x + l) 2 = 

Divide both sides by -|: (x + l) 2 = 
Take square root of both sides: x + l = 



-1 



The coordinates of the turning point are: (—1; —3). 
The i/-intercept is obtained by setting x = 0. This gives: 



Vint = -^(0 + l) 2 -3 

- -H 

- 4- 

_7 
2 



'12 



CHAPTER 11. QUADRATIC FUNCTIONS AND GRAPHS 



11.2 



The x-intercept is obtained by setting y = 0. This gives: 



= 


--(Xint + 1) - 


-3 


3 = 


— y{xint + 1) 




3.2 = 


{Xint + l) 2 




-6 = 


(.Xint + l) 2 





which has no real solutions. Therefore, there are no x-intercepts. 

We also know that the axis of symmetry is parallel to the y-axis and passes through the turning point. 




Figure 11.2: Graph of the function /(x) = -\{x + 1) -3 



© See video: VMfkk at www.everythingmaths.co.za 



Exercise 11 -5 



1. Draw the graph of y = 3(x — 2) 2 + 1 showing all the intercepts with the axes as well as the 
coordinates of the turning point. 



2. Draw a neat sketch graph of the function defined by y = ax 2 + bx + c if a > 0; 6 < 0; b 2 = Aac. 



(fie) More practice (►) video solutions ( ?) or help at www.everythingmaths 



(1.)011h (2.)011i 



93 



11.2 



CHAPTER 



QUADRATIC FUNCTIONS AND GRAPHS 



Writing an Equation of a Shifted Parabola 



EMBBC 



Given a parabola with equation y = x 2 — 2x — 3. The graph of the parabola is shifted one unit to the 
right. Or else the y-axis shifts one unit to the left i.e. x becomes x — 1. Therefore the new equation 
will become: 



y = (x-l) 2 -2(x-l)-3 
= x 2 - 2x + 1 - 2a; + 2 - 3 
= x — Ax 

If the given parabola is shifted 3 units down i.e. y becomes y + 3. The new equation will be: 
(Notice the x-axis then moves 3 units upwards) 



y + 'i 
y 



x — 2x — 3 
x — 2x — 6 



Chapter 1 1 



End of Chapter Exercises 



1. Show that if a < 0, then the range of /(x) = a(x+p) 2 +q is {f(x) : f(x) e (— oo,q]}. 

2. If (2; 7) is the turning point of /(x) = — 2x 2 —Aax + k, find the values of the constants 
a and k. 

3. The graph in the figure is represented by the equation f(x) = ax 2 + bx. The coordi- 
nates of the turning point are (3; 9). Show that a = — 1 and b = 6. 




4. Given: y = x — 2x + 3. Give the equation of the new graph originating if: 

(a) The graph of / is moved three units to the left. 

(b) The x-axis is moved down three units. 

5. A parabola with turning point (— 1; —4) is shifted vertically by 4 units upwards. What 
are the coordinates of the turning point of the shifted parabola? 



91 



CHAPTER 11. QUADRATIC FUNCTIONS AND GRAPHS 11.2 

\pc) More practice (►) video solutions ({J or help at www.everythingmaths.co.za 
(1 .) 01 Ij (2.) 011k (3.) 011m (4.)011n (5.)011p 



Do 



Hyperbolic Functions and 
Graphs 





12.1 Introduction 




In the previous chapter, we discussed the graphs of general quadratic functions. In this chapter we wil 
learn more about sketching and interpreting the graphs of general hyperbolic functions. 

See introductory video: VMfmc at www.everythingmaths.co.za 




12.2 Functions of the Form 



a 



x+p 



+ q 




This form of the hyperbolic function is slightly more complex than the form studied in Grade 1 0. 

5 




Figure 12.1: General shape and position of the graph of a function of the form f(x) = -^r — I- Q- The 
asymptotes are shown as dashed lines. 



Activity: 



Functions of the Form y — - s — + q 



96 



CHAPTER 12. HYPERBOLIC FUNCTIONS AND GRAPHS 



12.2 



1 . On the same set of axes, plot the following graphs: 

(a) a(x) = j=i + 1 

(b) b(x) = f± + 1 

(c) c(x) = ^ + 1 

(d) d{x) = j^r + l 

(e) e(x) = ^ + 1 

Use your results to deduce the effect of a. 

2. On the same set of axes, plot the following graphs: 



(a) f(x) = 


=b + l 


(b) g(x) = 


^T + l 


(c) h{x) = 


STo+1 


(d) j(x) = 


STT + 1 


(e) k(x) = 


SCT + 1 



Use your results to deduce the effect of p. 
3. Following the general method of the above activities, choose your own values of a and p 



to plot five different graphs of y ■■ 



q to deduce the effect of q. 



You should have found that the sign of a affects whether the graph is located in the first and third 
quadrants, or the second and fourth quadrants of Cartesian plane. 

You should have also found that the value of p affects whether the x-intercept is negative (p > 0) or 
positive (p < 0). 

You should have also found that the value of q affects whether the graph lies above the x-axis (q > 0) 
or below the x-axis (q < 0). 

These different properties are summarised in Table 12.1. The axes of symmetry for each graph is shown 
as a dashed line. 



Table 12.1: Table summarising general shapes and positions of functions of the form y = -^rr +q. The 
axes of symmetry are shown as dashed lines. 





p<0 


p> 




a > 


a < 


a > 


a < 


q>0 


■»—-=-; 




*=^^- 


r* 


-4 


^^=^ 


^i 


■^^* 




I 




f 


1 




i 

1 

r 




q<0 




i 
i 
i 


. 








i 
i 
.i 


, 


""? 




*=-==-: 


-L-^y 


4 


^^=^ 


i, 
'/ 


1 ■ 



97 



72.2 CHAPTER 12. HYPERBOLIC FUNCTIONS AND GRAPHS 



Domain and Range W embbf 



For y = -^r- + q, the function is undefined for x = —p. The domain is therefore 
{x : x e R,x ^ -p}. 

We see that y = -2 — |- q can be re-written as: 

a 

y 



x +p 
a 

V-1 = — : — 

x +p 

If x j^ —p then: (y — q)(x + p) = a 

a 

x + p = 

y-q 

This shows that the function is undefined at y = q. Therefore the range of f(x) = -^- — \- q is 
{f(x):f(x)eR,f(x)^q}. 

For example, the domain of g(x) = -£ri + 2 is {x : x e R, x =£ — 1} because g(x) is undefined at 
x=-l. 

2 
y = -— r + 2 
x + 1 

(2/ -2) 

)(* + !) 
(as + 1) 



x+l 
(y-2)(a; + l) 2 

2 



y-2 

We see that g(z) is undefined at y = 2. Therefore the range is {g(x) : g(x) G (— oo; 2) U (2; oo)}. 



Exercise 12-1 



1 . Determine the range of y = j + 1. 

2. Given:/(x) = ^r^ + 4. Write down the domain of /. 

3. Determine the domain of y = —^rj + 3 



fa+) More practice C ►) video solutions (9 J or help at www.everythingmaths.co.za 



(1.)01za (2.)01zb (3.) 01zc 



Intercepts wembbg 



For functions of the form, y = -^r — F q, the intercepts with the x and y axis are calculated by setting 
x = for the {/-intercept and by setting y = for the x-intercept. 



9S 



CHAPTER 12. HYPERBOLIC FUNCTIONS AND GRAPHS 



12.2 



The j/-intercept is calculated as follows: 



y 




X + p 


Vint 


= 


a 


+ p 




= 


a 

-+g 



(12.1) 
(12.2) 
(12.3) 



For example, the j/-intercept of g(x) = ^- + 2 is given by setting x = to get: 



y 


= 


x + l +2 




= 


2 I - 




0+1 




= 


T+ 2 




= 


2 + 2 



The x-intercepts are calculated by setting y = as follows: 

a 



'</ - 


x + p 











= 


a 




X int + p 




a 


= 






Zint +P 


Q 




a 


= 


-q(x lnt +p) 




Xj„t +p 


= 


a 



-'/ 



For example, the x-intercept of g(x) = ^- + 2 is given by setting x = to get: 



y 




x + 1 





= 


2 


X tnt + 1 


-2 


= 


2 


Xi„t + 1 


2(x int + 1) 


= 


2 


Xint + 1 


= 


2 

+2 


X i n 1 


= 


-1- 1 


X /;,)./ 


= 


-2 



(12.4) 

(12.5) 

(12.6) 

(12.7) 
(12.8) 

(12.9) 



Exercise 12-2 



1. Given: h(x) 



2. Determine the coordinates of the intercepts of h with the x- and y-axes. 



2. Determine the x-intercept of the graph of y = |+2. Give the reason why there is no y-intercept 
for this function. 



99 



72.2 CHAPTER 12. HYPERBOLIC FUNCTIONS AND GRAPHS 



A"0 More practice C ►) video solutions (9) or help at www.everythingmaths.co.: 



(1.)011q (2.)011r 



Asymptotes m embbh 



There are two asymptotes for functions of the form y = ^ — F ?■ They are determined by examining 
the domain and range. 

We saw that the function was undefined at x = — p and for y = q. Therefore the asymptotes are 
x = —p and y = q. 

For example, the domain of g(x) = j^ + 2 is {x : x e R;x ^ —1} because g(x) is undefined 
at x = — 1. We also see that g(x) is undefined at y = 2. Therefore the range is {g(x) : g(x) e 
(-oo;2)U(2;oo)}. 

From this we deduce that the asymptotes are at x = — 1 and y = 2. 



Exercise 12-3 



1 . Given: h(x) = -^-^ — 2. Determine the equations of the asymptotes of h. 

2. Write down the equation of the vertical asymptote of the graph y = — ^-. 

fa+) More practice C ►) video solutions (9) or help at www.everythingmaths.co.za 
(1.)01zd (2.)01ze 

Sketching Graphs of the Form f(x) = ^-+q m embbi 



In order to sketch graphs of functions of the form, f(x) = -^- + q, we need to calculate four charac- 
teristics: 

1. domain and range 

2. asymptotes 

3. ^/-intercept 

4. x-intercept 



100 



CHAPTER 12. HYPERBOLIC FUNCTIONS AND GRAPHS 



12.2 



For example, sketch the graph of g(x) = jrfj + 2. Mark the intercepts and asymptotes. 

We have determined the domain to be {x : x e R, x =£ — 1} and the range to be {g(x) : g(x) e 
(— oo; 2) U (2; oo)}. Therefore the asymptotes are at x = — 1 and y = 2. The ?/-intercept = 4 and the 
x-intercept = —2. 




H 1 1 h 

12 3 4 



Figure 1 2.2: Graph of g(x) = ^- + 2. 



Exercise 12-4 



1 . Draw the graph of y = - + 2. Indicate the horizontal asymptote. 



2. Given: h(x) = -£-^ — 2. Sketch the graph of h showing clearly the asymptotes and ALL intercepts 
with the axes. 



3. Draw the graph of y = i and y = — jrfrj- + 3 on the same system of axes. 



4. Draw the graph of y = x _ 5 2 5 + 2. Explain your method. 



5. Draw the graph of the function defined by y = ^^ + 4. Indicate the asymptotes and intercepts 
with the axes. 



101 



72.2 



CHAPTER 12. HYPERBOLIC FUNCTIONS AND GRAPHS 



A"y More practice f ►) video solutions f 9j or help at www.everythingmaths.co.: 



(1.) Oils (2.) Ol1t (3.)011u (4.)011v (5.)011w 



Chapter 1 2 



End of Chapter Exercises 



1. Plot the graph of the hyperbola defined by y = | for — 4 < x < 4. Suppose the 
hyperbola is shifted 3 units to the right and 1 unit down. What is the new equation 
then? 

2. Based on the graph of y = |, determine the equation of the graph with asymptotes 
y = 2 and x = 1 and passing through the point (2; 3). 



Q\+) More practice (►) video solutions Cf) or help at www.everythingmaths.co.za 



(l.)011x (2.) Oily 



102 



Exponential Functions an 
Graphs 





13.1 Introduction 




Building on the previous two chapters, we will discuss the sketching and interpretation of the graphs 
of general exponential functions in this chapter. 

© See introductory video: VMfmg at www.everythingmaths.co.za 



13.2 Functions of the Form 

= ab( x+ ^ + q for b > 




This form of the exponential function is slightly more complex than the form studied in Grade 10. 




H 1 1 r 

-4 -3 -2 -1 



12 3 4 



Figure 13.1: General shape and position of the graph of a function of the form f(x) = ab^ x+p} + q. 



Activity: 



Functions of the Form y = ab^ x+p ^ + q 



1 . On the same set of axes, plot the following graphs: 

(a) a(x) = -2 {x+1) + 1 

(b) b(x) =-l< a,+1 >+l 

(c) d(x) = l (x+1) + 1 

(d) e{x) = 2 {x+1) + 1 

Use your results to deduce the effect of a. 

2. On the same set of axes, plot the following graphs: 

(a) f(x) = 2 (x+1) - 2 



1 03 



13.2 



CHAPTER 13. EXPONENTIAL FUNCTIONS AND GRAPHS 



(b) g(x) = 2 {x+1) - 1 

(c) h(x) = 2 (x+1) + 

(d) j(x) = 2 {x+1) + 1 

(e) k(x) = 2 (x+1) + 2 

Use your results to deduce the effect of q. 

3. Following the general method of the above activities, choose your own values of a and q 
to plot five different graphs of y = ab^ x+p) + q to deduce the effect of p. 

You should have found that the value of a affects whether the graph is above the asymptote (a > 0) or 
below the asymptote (a < 0). 

You should have also found that the value of p affects the position of the x-intercept. 

You should have also found that the value of q affects the position of the y-intercept. 

These different properties are summarised in Table 13.1. The axes of symmetry for each graph is shown 
as a dashed line. 

Table 13.1: Table summarising general shapes and positions of functions of the formy = a6 (a:+p) + q. 





p<0 


p > 




a > 


a < 


a > 


a < 


q>0 










S 


n 






















q<0 












[/ 












\ 


A 


/ * 




X 



Domain and Range 



EMBBL 



For y = afe (a:+p) + q, the function is defined for all real values of x. Therefore, the domain is {x : x e 

K}. 

The range of y = ab i - x+p ^ + q is dependent on the sign of a. 
If a > then: 

a . b {x+p) > 

a.b {x+p) +q > q 

fix) > q 

Therefore, if a > 0, then the range is {/(x) : f{x) € [q; oo)}. 



104 



CHAPTER 13. EXPONENTIAL FUNCTIONS AND GRAPHS 13.2 

If a < then: 

b (*+P) > 

a . b (x+p) < 
a . b {x+p) +q < q 
f(x) < q 
Therefore, if a < 0, then the range is {/(x) : f{x) e (— oo; g]}. 
For example, the domain of g{x) = 3 . 2 X+1 + 2 \s {x : x £ R}. For the range, 

2 X+1 > 

3 . 2 1+1 > 

3.2 a,+1 +2 > 2 

Therefore the range is {g(x) : g{x) e [2; oo)}. 



Exercise 13-1 



1 . Give the domain of y = 3 1 . 

2. What is the domain and range of f(x) = 2 X ? 

3. Determine the domain and range of y = (l,5) x+3 . 



Q\n More practice (V) video solutions C{) or help at www.everythingmaths.co.za 



(1.)011z (2.) 0120 (3.) 0121 



Intercepts wembbm 



For functions of the form, y = ab^ x+p) + q, the intercepts with the x- and y-axis are calculated by 
setting x = for the y-intercept and by setting y = for the x-intercept. 

The j/-intercept is calculated as follows: 



y = ab {x+p) +q (13.1) 

nt = ab {0+p) +q (13.2) 

= ab p +q (13.3) 



For example, the y-intercept of g(x) = 3 . 2 X+1 + 2 is given by setting x = to get: 

y = 3.2* +1 +2 

Vint = 3.2 0+1 +2 

= 3.2 J +2 

= 3.2 + 2 

= 8 



105 



13.2 CHAPTER 13. EXPONENTIAL FUNCTIONS AND GRAPHS 

The x-intercepts are calculated by setting y = as follows: 

y = ab {x+p) +q (13.4) 

= ab lXi " t+p) + q (13.5) 

a6 C**„«+P) = _ q (136) 

b (x int +p) = _1 (137) 

a 
Which only has a real solution if either a < or q < and a^O. Otherwise, the graph of the function 
of form y = a6 (x+p) + q does not have any x-intercepts. 

For example, the x-intercept of g(x) = 3 . 2 X+1 + 2 is given by setting y = to get: 

y = 3.2* +1 +2 
= 3.2 a; '" t+1 +2 
-2 = 3.2 Ii «' +1 

" 3 
which has no real solution. Therefore, the graph of g(x) = 3 . 2 X+1 + 2 does not have a x-intercept. 



Exercise 13-2 



1 . Give the j/-intercept of the graph of y = b x + 2. 

2. Give the x- and j/-intercepts of the graph of y = ^(l,5) x+3 — 0,75. 



U\"y More practice (►) video solutions (9) or help at www.everythingmaths.co.za 



(1.) 0122 (2.) 0123 



Asymptotes w embbn 



The asymptote is the place at which the function is undefined. For functions of the form y = ab ( - x+p> +q 
this is along the line where y = q. 

For example, the asymptote of g{x) = 3 . 2 X+1 + 2 is y = 2. 



Exercise 13-3 



1 . Give the equation of the asymptote of the graph of y = 3 X — 2. 

2. What is the equation of the horizontal asymptote of the 
graph of y = 3(0,S) x - 1 -3? 



A"y More practice (►) video solutions (9j or help at www.everythingmaths 



(1.) 0124 (2.) 0125 



106 



CHAPTER 13. EXPONENTIAL FUNCTIONS AND GRAPHS 



13.2 



Sketching Graphs of the Form f(x 

a^x+v) + q 



EMBBO 



In order to sketch graphs of functions of the form, f(x) = ab l - x+p) + q, we need to determine four 
characteristics: 

1 . domain and range 

2. ^-intercept 

3. x-intercept 

For example, sketch the graph of g(x) = 3 . 2 X+1 + 2. Mark the intercepts. 

We have determined the domain to be {x : x e R} and the range to be {g(x) : g(x) e (2; oo)}. 

The j/-intercept is y tn t = 8 and there is no x-intercept. 




H 1 1 \ 

-4 -3 -2 -1 



Figure 13.2: Graph of g{x) = 3 . 2 a=+1 + 2. 



Exercise 13 -4 



1 . Draw the graphs of the following on the same set of axes. Label the horizontal asymptotes and 
y-intercepts clearly. 

(a) y = 2* + 2 

(b) y = T+ 2 



107 



13.2 



CHAPTER 13. EXPONENTIAL FUNCTIONS AND GRAPHS 



(c) y = 2 . 2* 

(d) y = 2. 2*+ 2 + 2 

2. Draw the graph of /(&) = 3*. 

3. Explain where a solution of 3" = 5 can be read off the graph. 



A"y More practice CrJ video solutions ({J or help at www.everythingmaths 



(1.)01zf (2.)01zg (3.)01zh 



Chapter 1 3 



End of Chapter Exercises 



1. The following table of values has columns giving the ^-values for the graph y = a x , 
y = a x+1 and y = a x + 1. Match a graph to a column. 



X 


A 


B 


C 


-2 


7.2o 


6,25 


2,5 


-1 


3,5 


2,5 


1 





2 


1 


0,4 


1 


1.1 


0,4 


0,16 


2 


1,16 


0,16 


0,064 



2. The graph of f(x) = 1 + a.2 x (a is a constant) passes through the origin. 

(a) Determine the value of a. 

(b) Determine the value of /(— 15) correct to five decimal places. 

(c) Determine the value of x, if P(x; 0,5) lies on the graph of /. 

(d) If the graph of / is shifted 2 units to the right to give the function h, write down 
the equation of h. 

3. The graph of f(x) = a.b x (a ^ 0) has the point P(2; 144) on /. 

(a) If b = 0,75, calculate the value of a. 

(b) Hence write down the equation of /. 

(c) Determine, correct to two decimal places, the value of /(13). 

(d) Describe the transformation of the curve of / to h if h(x) = /(— x). 



\Pc) More practice (►) video solutions (?J or help at www.everythingmaths.co.za 



(1.) 0127 (2.) 0128 (3.) 0129 



ION 



Gradient at a Point 





14.1 Introduction 




In Grade 1 0, we investigated the idea of average gradient and saw that the gradients of most functions 
varied over different intervals. In Grade 11, we discuss the concept of average gradient further, and 
introduce the idea of the gradient of a curve at a point. 

© See introductory video: VMfns at www.everythingmaths.co.za 




14.2 Average Gradient 




We saw that the average gradient between two points on a curve is the gradient of the straight line 
passing through the two points. 



^(-3; 7) 




C(-l;-l) 



Figure 14.1: The average gradient between two points on a curve is the gradient of the straight line 
that passes through the points. 



What happens to the gradient if we fix the position of one point and move the second point closer to 
the fixed point? 



Activity: 



Gradient at a Single Point on a Curve 






The curve shown below is defined by y = — 2x 2 — 5. Point B is fixed at coordinates (0; —5). 
The position of point A varies. Complete the table below by calculating the ^-coordinates of 
point A for the given x-coordinates and then calculate the average gradient between points A 
and B. 



109 



74.2 



CHAPTER 14. GRADIENT AT A POINT 



XA 


VA 


average gradient 


-2 






-1.5 






-1 






-0.5 













0.5 






1 






1.5 






2 








What happens to the average gradient as A moves towards _B? What happens to the average 
gradient as A moves away from _B? What is the average gradient when A overlaps with £>? 



In Figure 14.2, the gradient of the straight line that passes through points A and C changes as A moves 
closer to C. At the point when A and C overlap, the straight line only passes through one point on the 
curve. Such a line is known as a tangent to the curve. 




(a) 



(b) 



\ y 




\a 




c\ 


1 x 







(0 



(d) 





Figure 14.2: The gradient of the straight line between A and C changes as the point A moves along 
the curve towards C. There comes a point when A and C overlap (as shown in (c)). At this point the 
line is a tangent to the curve. 

We therefore introduce the idea of a gradient at a single point on a curve. The gradient at a point on a 
curve is simply the gradient of the tangent to the curve at the given point. 



110 



CHAPTER 14. GRADIENT AT A POINT 14.2 



Example 1: Average Gradient 



QUESTION 



Find the average gradient between two points P(a; g(a)) and Q(a + h; g(a + h)) on a curve 
g(x) = x 2 . Then find the average gradient between P(2; g(2)) and Q(4; g(4)). Finally, explain 
what happens to the average gradient if P moves closer to Q. 



SOLUTION 



Step 1 : Label x points 

x\ = a 
X2 = a + h 

Step 2 : Determine y coordinates 

Using the function g(x) = x 2 , we can determine: 

2/i = 3(a) = o 2 

2/2 = g(a + h) 

= {a + hf 



Step 3 : Calculate average gradient 

2/2 -2/1 (a 2 + 2ah + h 2 ) - (a 2 ) 

x 2 — Xi (a + h) — (a) 

a 2 + 2ah + h 2 - a 2 



a + h — a 
2ah + h 2 



h 
h(2a + h) 
h 
= 2a + h (14.1) 

The average gradient between P(a;g(a)) and Q(a + h;g(a + h)) on the 
curve g(x) = x 2 is 2a + h. 

Step 4 : Calculate the average gradient between P(2; g(2)) and Q(4; g(A)) 

We can use the result in (14.1), but we have to determine what a and h are. We 
do this by looking at the definitions of P and Q. The x-coordinate of P is a and 
the x-coordinate of Q is a + h therefore if we assume that a = 2 and o + h = 4, 
then h = 2. 

Then the average gradient is: 

2a + h = 2(2) + (2) = 6 
Step 5 : When P moves closer to Q 



111 



14.2 CHAPTER 14. GRADIENT AT A POINT 



When point P moves closer to point Q, h gets smaller. This means that the 
average gradient also gets smaller. When the point Q overlaps with the point P 
h = and the average gradient is given by 2a. 



We now see that we can write the equation to calculate average gradient in a slightly different manner. 
If we have a curve defined by f(x) then for two points P and Q with P(a; /(a)) and Q(a+h; f(a+h)), 
then the average gradient between P and Q on f(x) is: 

V2 -yi f{a + h) - f{a) 

X2 — xi (a + h) — (a) 

f{a + h)-f(a) 
h 

This result is important for calculating the gradient at a point on a curve and will be explored in greater 
detail in Grade 12. 



Chapter 14 



End of Chapter Exercises 



1. (a) Determine the average gradient of the curve f(x) = x(x + 3) between x = 5 

and x = 3. 
(b) Hence, state what you can deduce about the function / between x = 5 and 
x = 3. 

2. A(1;3) is a point on f(x) = 3x 2 . 

(a) Determine the gradient of the curve at point A. 

(b) Hence, determine the equation of the tangent line at A. 

3. Given: f(x) = 2x 2 . 

(a) Determine the average gradient of the curve between x = — 2 and x = 1. 

(b) Determine the gradient of the curve of / where x = 2. 



UX*) More practice (►) video solutions (9) or help at www.everythingmaths.co.za 
(l.)012a (2.) 012b (3.) 012c 



112 



Linear Programming 





1 5. 7 Introduction 




In everyday life people are interested in knowing the most efficient way of carrying out a task or 
achieving a goal. For example, a farmer might want to know how many crops to plant during a season 
in order to maximise yield (produce) or a stock broker might want to know how much to invest in 
stocks in order to maximise profit. These are examples of optimisation problems, where by optimising 
we mean finding the maxima or minima of a function. 

See introductory video: VMfnt at www.everythingmaths.co.za 




15.2 Terminology 




There are some basic terms which you need to become familiar with for the linear programming 
chapters. 



Decision Variabies 



EMBBT 



The aim of an optimisation problem is to find the values of the decision variables. These values are 
unknown at the beginning of the problem. Decision variables usually represent things that can be 
changed, for example the rate at which water is consumed or the number of birds living in a certain 
park. 



Objective Function 



EMBBU 



The objective function is a mathematical combination of the decision variables and represents the 
function that we want to optimise (i.e. maximise or minimise). We will only be looking at objective 
functions which are functions of two variables. For example, in the case of the farmer, the objective 
function is the yield and it is dependent on the amount of crops planted. If the farmer has two crops 
then the objective function f(x,y) is the yield, where x represents the amount of the first crop planted 
and y represents the amount of the second crop planted. For the stock broker, assuming that there are 
two stocks to invest in, the objective function f(x,y) is the amount of profit earned by investing x rand 
in the first stock and y rand in the second. 



1 1 3 



75.2 



CHAPTER 15. LINEAR PROGRAMMING 



Constraints 



EMBBV 



Constraints, or restrictions, are often placed on the variables being optimised. For the example of the 
farmer, he cannot plant a negative number of crops, therefore the constraints would be: 

x > 
y>0. 

Other constraints might be that the farmer cannot plant more of the second crop than the first crop and 
that no more than 20 units of the first crop can be planted. These constraints can be written as: 

x>y 
x < 20 



Constraints that have the form 



ax + by < c 



ax + by = c 
are called linear constraints. Examples of linear constraints are: 

x + y < 

-2x = 7 

y<sfi 



Feasible Region and Points 



EMBBW 



Tip 



The constraints are used 
to create bounds of the 
solution. 



Tip 



Points that satisfy the 
constraints are called 
feasible solutions. 



Constraints mean that we cannot just take any x and y when looking for the x and y that optimise our 
objective function. If we think of the variables x and y as a point {x,y) in the xj/-plane then we call 
the set of all points in the xy-p\ane that satisfy our constraints the feasible region. Any point in the 
feasible region is called a feasible point. 

For example, the constraints 

x > 

y>o. 

mean that only values of x and y that are positive are allowed. Similarly, the constraint 

x>y 
means that only values of x that are greater than or equal to the y values are allowed. 

x < 20 
means that only x values which are less than or equal to 20 are allowed. 



Ill 



CHAPTER 15. LINEAR PROGRAMMING 



15.3 



The Solution 



EMBBX 



Once we have determined the feasible region the solution of our problem will be the feasible point 
where the objective function is a maximum / minimum. Sometimes there will be more than one 
feasible point where the objective function is a maximum/minimum — in this case we have more than 
one solution. 




1 5.3 Example of a Problem 




A simple problem that can be solved with linear programming involves Mrs Nkosi and her farm. 



Mrs Nkosi grows mielies and potatoes on a farm of 100 m 2 . She has accepted orders that 
will need her to grow at least 40 m 2 of mielies and at least 30 m 2 of potatoes. Market 
research shows that the demand this year will be at least twice as much for mielies as for 
potatoes and so she wants to use at least twice as much area for mielies as for potatoes. 
She expects to make a profit of R650 per m 2 for her mielies and Rl 500 per m 2 on her 
potatoes. How should she divide her land so that she can earn the most profit? 



Let q represent the area of mielies grown and let p be the area of potatoes grown. 
We shall see below how we can solve this problem. 




1 5.4 Method of Linear 
Programming 




Method: Linear Programming 



EMBCA 



1 . Identify the decision variables in the problem. 



2. Write constraint equations 



3. Write objective function as an equation 



4. Solve the problem 



115 



75.5 



CHAPTER 75. LINEAR PROGRAMMING 




15.5 Skills You Will Need 




Writing Constraint Equations 



EMBCC 



You will need to be comfortable with converting a word description to a mathematical description for 
linear programming. Some of the words that are used is summarised in Table 1 5.1 . 



Table 15.1: Phrases and mathematical equivalents. 



Words 


Mathematical description 


x equals a 


x = a 


x is greater than a 


x > a 


x is greater than or equal to a 


x > a 


x is less than a 


x < a 


x is less than or equal to a 


x < a 


x must be at least a 


x > a 


x must be at most a 


x < a 



Example 1: Writing constraints as equations 



QUESTION 



Mrs Nkosi grows mielies and potatoes on a farm of 100 m 2 . She has accepted orders that will 
need her to grow at least 40 m 2 of mielies and at least 30 m 2 of potatoes. Market research 
shows that the demand this year will be at least twice as much for mielies as for potatoes and 
so she wants to use at least twice as much area for mielies as for potatoes. 



SOLUTION 



Step 7 : Identify the decision variables 

There are two decision variables: the area used to plant mielies (q) and the area 
used to plant potatoes (p). 



Step 2 : Identify the phrases that constrain the decision variables 

• grow at least 40 m 2 of mielies 

• grow at least 30 m 2 of potatoes 

• area of farm is 100 m 2 

• demand is at least twice as much for mielies as for potatoes 

Step 3 : For each phrase, write a constraint 



116 



CHAPTER 15. LINEAR PROGRAMMING 15.5 




Exercise 15-1 



Write the following constraints as equations: 

1 . Michael is registering for courses at university. Michael needs to register for at least 4 courses. 

2. Joyce is also registering for courses at university. She cannot register for more than 7 courses. 

3. In a geography test, Simon is allowed to choose 4 questions from each section. 

4. A baker can bake at most 50 chocolate cakes in one day. 

5. Megan and Katja can carry at most 400 koeksisters. 

fA J More practice Cr) video solutions ("fj or help at www.everythingmaths.co.za 
(1.)012d (2.)012e (3.) 01 2f (4.) 012g (5.) 012h 



Writing the Objective Function W embcd 



If the objective function is not given to you as an equation, you will need to be able to convert a word 
description to an equation to get the objective function. 

You will need to look for words like: 

• most profit 

• least cost 

• largest area 



117 



75.5 CHAPTER 15. LINEAR PROGRAMMING 



Example 2: Writing the objective function 



QUESTION 



The cost of hiring a small trailer is R500 per day and the cost of hiring a big trailer is R800 per 
day. Write down the objective function that can be used to find the cheapest cost for hiring 
trailers for one day. 



SOLUTION 



Step 1 : Identify the decision variables 

There are two decision variables:the number of small trailers (to) and the number 
of big trailers (n). 

Step 2 : Write the purpose of the objective function 

The purpose of the objective function is to minimise cost. 

Step 3 : Write the objective function 

The cost of hiring m small trailers for one day is: 

500 x m 
The cost of hiring n big trailers for one day is: 

800 x n 

Therefore the objective function, which is the total cost of hiring m small trailers 
and n big trailers for one day is: 

(500 x to) + (800 x n) 



Example 3: Writing the objective function 



QUESTION 



Mrs Nkosi expects to make a profit of R650 per m 2 for her mielies and Rl 500 per m 2 on her 
potatoes. How should she divide her land so that she can earn the most profit? 



118 



CHAPTER 15. LINEAR PROGRAMMING 15.5 



SOLUTION 


Step 1 


: Identify the decision variables 

There are two decision variables: the area used to plant mielies 
used to plant potatoes (p). 


(q) and the 


area 


Step 2 


: Write the purpose of the objective function 

The purpose of the objective function is to maximise profit. 






Step 3 


: Write the objective function 

The profit of planting q m 2 of mielies is: 

650 X q 
The profit of planting p m 2 of potatoes is: 
1 500 x p 








Therefore the objective function, which is the total profit of planting mielies 
potatoes is: 

(650 X q) + (1 500 x p) 


and 





Exercise 15-2 



1 . The EduFurn furniture factory manufactures school chairs and school desks. They make a profit 
of R50 on each chair sold and of R60 on each desk sold. Write an equation that will show how 
much profit they will make by selling the chairs and desks. 

2. A manufacturer makes small screen GPS units and wide screen GPS units. If the profit on a small 
screen GPS unit is R500 and the profit on a wide screen GPS unit is R250, write an equation that 
will show the possible maximum profit. 



A"j More practice f ►) video solutions f? j or help at www.everythingmaths.co.za 



(1.)012i (2.) 012j 



Solving the Problem W embce 



The numerical method involves using the points along the boundary of the feasible region, and deter- 
mining which point optimises the objective function. 



119 



75.5 



CHAPTER 75. LINEAR PROGRAMMING 



Activity: 



Numerical Method 



Use the objective function 

(650 x q) + (1 500 x p) 
to calculate Mrs Nkosi's profit for the following feasible solutions: 



<? 


/' 


Profit 


60 


30 




65 


30 




70 


30 




66^ 


33 f 





The question is how do you find the feasible region? We will use the graphical method of solving 
a system of linear equations to determine the feasible region. We draw all constraints as graphs and 
mark the area that satisfies all constraints. This is shown in Figure 1 5.1 for Mrs Nkosi's farm. 




* V 



10 20 



40 50 



80 90 100 



Figure 15.1: Graph of the feasible region 



Vertices (singular: vertex) are the points on the graph where two or more of the constraints overlap or 
cross. If the linear objective function has a minimum or maximum value, it will occur at one or more 
of the vertices of the feasible region. 

Now we can use the methods we learnt previously to find the points at the vertices of the feasible 
region. In Figure 15.1, vertex A is at the intersection of p = 30 and q = 2p. Therefore, the coordinates 
of A are (30; 60). Similarly vertex B is at the intersection of p = 30 and q = 100 — p. Therefore the 
coordinates of B are (30; 70). Vertex C is at the intersection of q = 100 — p and q = 2p, which gives 
(33 1 ; 66|) for the coordinates of C. 

If we now substitute these points into the objective function, we get the following: 



120 



CHAPTER 15. LINEAR PROGRAMMING 



15.5 



1 


P 


Profit 


60 


30 


81000 


70 


30 


87 000 


66 1 


33 1 


89 997 



Therefore Mrs Nkosi makes the most profit if she plants 66§ m 2 of mielies and 33| m 2 of potatoes. 
Her profit is R89 997. 



Example 4: Prizes! 



QUESTION 



As part of their opening specials, a furniture store has promised to give away at least 40 prizes 
with a total value of at least R2 000. The prizes are kettles and toasters. 

1 . If the company decides that there will be at least 10 of each prize, write down two more 
inequalities from these constraints. 

2. If the cost of manufacturing a kettle is R60 and a toaster is R50, write down an objective 
function C which can be used to determine the cost to the company of both kettles and 
toasters. 

3. Sketch the graph of the feasibility region that can be used to determine all the possible 
combinations of kettles and toasters that honour the promises of the company. 

4. How many of each prize will represent the cheapest option for the company? 

5. How much will this combination of kettles and toasters cost? 



SOLUTION 



Step 1 : Identify the decision variables 

Let the number of kettles be x and the number of toasters be y and write down 
two constraints apart from x > and y > that must be adhered to. 



Step 2 : Write constraint equations 

Since there will be at least 10 of each prize we can write: 



x > 10 



and 



j/>10 
Also the store has promised to give away at least 40 prizes in total. Therefore: 

x + y > 40 

Step 3 : Write the objective function 

The cost of manufacturing a kettle is R60 and a toaster is R50. Therefore the cost 
the total cost C is: 

C = 60x + 50?/ 

Step 4 : Sketch the graph of the feasible region 



121 



75.5 



CHAPTER 75. LINEAR PROGRAMMING 

























90 - 




















80 - 






















70 - 






















60 - 






















50 - 






















40 - 






















30 - 




B 


















20 - 






\A 




















\ 




1 


1 
20 


i 
30 


40 


50 


60 


70 


80 


90 


* 
100 



Step 5 : Determine vertices of feasible region 

From the graph, the coordinates of vertex A are (30; 10) and the coordinates of 
vertex B are (10; 30). 



Step 6 : Calculate cost at each vertex 

At vertex A, the cost is: 

C = 60x + 50j/ 

= 60(30) + 50(10) 

= 1 800 + 500 

= 2 300 

At vertex B, the cost is: 

C* = 60x + 50j/ 

= 60(10) + 50(30) 

= 600 + 1 500 

= 2 100 

Step 7 : Write the final answer 

The cheapest combination of prizes is 10 kettles and 30 toasters, costing the 
company R2 100. 



Chapter 1 5 



End of Chapter Exercises 



122 



CHAPTER 15. LINEAR PROGRAMMING 



15.5 



1. You are given a test consisting of two sections. The first section is on algebra and 
the second section is on geometry. You are not allowed to answer more than 10 
questions from any section, but you have to answer at least 4 algebra questions. The 
time allowed is not more than 30 minutes. An algebra problem will take 2 minutes 
and a geometry problem will take 3 minutes to solve. 

If you answer x algebra questions and y geometry questions, 

(a) Formulate the constraints which satisfy the above constraints. 

(b) The algebra questions carry 5 marks each and the geometry questions carry 10 
marks each. If T is the total marks, write down an expression for T. 

2. A local clinic wants to produce a guide to healthy living. The clinic intends to pro- 
duce the guide in two formats: a short video and a printed book. The clinic needs to 
decide how many of each format to produce for sale. Estimates show that no more 
than 10 000 copies of both items together will be sold. At least 4 000 copies of the 
video and at least 2 000 copies of the book could be sold, although sales of the book 
are not expected to exceed 4 000 copies. Let x be the number of videos sold, and y 
the number of printed books sold. 

(a) Write down the constraint inequalities that can be deduced from the given infor- 
mation. 

(b) Represent these inequalities graphically and indicate the feasible region clearly. 

(c) The clinic is seeking to maximise the income, /, earned from the sales of the 
two products. Each video will sell for R50 and each book for R30. Write down 
the objective function for the income. 

(d) What maximum income will be generated by the two guides? 

3. A patient in a hospital needs at least 18 grams of protein, 0,006 grams of vitamin 
C and 0,005 grams of iron per meal, which consists of two types of food, A and 
B. Type A contains 9 grams of protein, 0,002 grams of vitamin C and no iron per 
serving. Type B contains 3 grams of protein, 0,002 grams of vitamin C and 0,005 
grams of iron per serving. The energy value of A is 800 kilojoules and of B 400 
kilojoules per serving. A patient is not allowed to have more than 4 servings of A 
and 5 servings of B. There are x servings of A and y servings of B on the patient's 
plate. 

(a) Write down in terms of x and y 

i. The mathematical constraints which must be satisfied, 
ii. The kilojoule intake per meal. 

(b) Represent the constraints graphically on graph paper. Use the scale 1 unit = 
20mm on both axes. Shade the feasible region. 

(c) Deduce from the graphs, the values of x and y which will give the minimum 
kilojoule intake per meal for the patient. 

4. A certain motorcycle manufacturer produces two basic models, the Super X and the 
Super Y. These motorcycles are sold to dealers at a profit of R20 000 per Super X and 
R10 000 per Super Y. A Super X requires 150 hours for assembly, 50 hours for painting 
and finishing and 10 hours for checking and testing. The Super Y requires 60 hours for 
assembly, 40 hours for painting and finishing and 20 hours for checking and testing. 
The total number of hours available per month is: 30 000 in the assembly department, 
13 000 in the painting and finishing department and 5 000 in the checking and testing 
department. 

The above information can be summarised by the following table: 



Department 


Hours for Super X 


Hours for Super Y 


Maximum hours avail- 
able per month 


Assembly 


150 


60 


30 000 


Painting and Finishing 


50 


40 


13 000 


Checking and Testing 


10 


20 


5 000 



123 



75.5 



CHAPTER 15. LINEAR PROGRAMMING 



Letx be the number of Super X and y be the number of Super V models manufactured 
per month. 

(a) Write down the set of constraint inequalities. 

(b) Use the graph paper provided to represent the constraint inequalities. 

(c) Shade the feasible region on the graph paper. 

(d) Write down the profit generated in terms of x and y. 

(e) How many motorcycles of each model must be produced in order to maximise 
the monthly profit? 

(f) What is the maximum monthly profit? 

5. A group of students plan to sell x hamburgers and y chicken burgers at a rugby match. 
They have meat for at most 300 hamburgers and at most 400 chicken burgers. Each 
burger of both types is sold in a packet. There are 500 packets available. The demand 
is likely to be such that the number of chicken burgers sold is at least half the number 
of hamburgers sold. 

(a) Write the constraint inequalities. 

(b) Two constraint inequalities are shown on the graph paper provided. Represent 
the remaining constraint inequalities on the graph paper. 

(c) Shade the feasible region on the graph paper. 

(d) A profit of R3 is made on each hamburger sold and R2 on each chicken burger 
sold. Write the equation which represents the total profit P in terms of x and y. 

(e) The objective is to maximise profit. How many, of each type of burger, should 
be sold to maximise profit? 

6. Fashion-cards is a small company that makes two types of cards, type X and type Y. 
With the available labour and material, the company can make not more than 150 
cards of type X and not more than 120 cards of type Y per week. Altogether they 
cannot make more than 200 cards per week. 

There is an order for at least 40 type X cards and 10 type Y cards per week. Fashion- 
cards makes a profit of R5 for each type X card sold and R10 for each type Y card. 
Let the number of type X cards be x and the nu 

y 

























90 - 




















80 - 






















70 - 






















60 - 






















50 - 






















40 - 






















30 - 




B 


















20 - 




























\ A 




















I i \i i i i i i i . 




1 


1 
20 


i 
30 


40 


i 
50 


i 
60 


i 
70 


i 
80 


i 
90 


i - 
100 



mber of type Y cards be y, manufactured per week. 

(a) One of the constraint inequalities which represents the restrictions above is x < 
150. Write the other constraint inequalities. 



121 



CHAPTER 15. LINEAR PROGRAMMING 



15.5 



(b) Represent the constraints graphically and shade the feasible region. 

(c) Write the equation that represents the profit P (the objective function), in terms 
of x and y. 

(d) Calculate the maximum weekly profit. 

7. To meet the requirements of a specialised diet a meal is prepared by mixing two 
types of cereal, Vuka and Molo. The mixture must contain x packets of Vuka cereal 
and y packets of Molo cereal. The meal requires at least 15 g of protein and at least 
72 g of carbohydrates. Each packet of Vuka cereal contains 4 g of protein and 16 
g of carbohydrates. Each packet of Molo cereal contains 3 g of protein and 24 g of 
carbohydrates. There are at most 5 packets of cereal available. The feasible region is 
shaded on the attached graph paper. 

(a) Write down the constraint inequalities. 

(b) If Vuka cereal costs R6 per packet and Molo cereal also costs R6 per packet, use 
the graph to determine how many packets of each cereal must be used for the 
mixture to satisfy the above constraints in each of the following cases: 

i. The total cost is a minimum, 
ii. The total cost is a maximum (give all possibilities). 




12 3 4 5 

Number of packets of Vuka 



A bicycle manufacturer makes two different models of bicycles, namely mountain 
bikes and speed bikes. The bicycle manufacturer works under the following con- 
straints: 

No more than 5 mountain bicycles can be assembled daily. 
No more than 3 speed bicycles can be assembled daily. 

It takes one man to assemble a mountain bicycle, two men to assemble a speed bi- 
cycle and there are 8 men working at the bicycle manufacturer. 
Let x represent the number of mountain bicycles and let y represent the number of 
speed bicycles. 

(a) Determine algebraically the constraints that apply to this problem. 

(b) Represent the constraints graphically on the graph paper. 

(c) By means of shading, clearly indicate the feasible region on the graph. 

(d) The profit on a mountain bicycle is R200 and the profit on a speed bicycle is 
R600. Write down an expression to represent the profit on the bicycles. 

(e) Determine the number of each model bicycle that would maximise the profit to 
the manufacturer. 



125 



75.5 CHAPTER 15. LINEAR PROGRAMMING 



Q\+) More practice f ►) video solutions Cfj or help at www.everythingmaths.co.za 



(1.) 012k (2.) 012m (3.)012n (4.) 012p (5.) 012q (6.)012r 
(7.) 012s (8.)012t 



120 



Geometry 





1 6. 1 Introduction 




Geometry is a good subject for learning not just about the mathematics of two and three-dimensional 
shapes, but also about how we construct mathematical arguments. In this chapter you will learn how 
to prove geometric theorems and discover some of the properties of shapes through small logical steps. 

© See introductory video: VMfqd at www.everythingmaths.co.za 




16.2 Right Pyramids, Right Cones 
and Spheres 



A pyramid is a geometric solid that has a polygon base and the base is joined to a point, called the 
apex. Two examples of pyramids are shown in the left-most and centre figures in Figure 16.1. The 
right-most figure has an apex which is joined to a circular base and this type of geometric solid is 
called a cone. Cones are similar to pyramids except that their bases are circles instead of polygons. 






Figure 1 6.1 : Examples of a square pyramid, a triangular pyramid and a cone. 

Surface Area of a Pyramid 

The surface area of a pyramid is calculated by adding the area of each face together. 



Example 1: 


Surface Area 


















QUESTION 


If a cone has 

irr\/r 2 + h 2 . 


a height of h and a 


base of radius r, 


show that the 


surface 


area 


is 


nr 2 


+ 



127 



16.2 



CHAPTER 16. GEOMETRY 



SOLUTION 



Step 1 : Draw a picture 




Step 2 : Identify the faces that make up the cone 

The cone has two faces: the base and the walls. The base is a circle of radius r 
and the walls can be opened out to a sector of a circle. 





27rr = circumference 

This curved surface can be cut into many thin triangles with height close to a (a is 
called the slant height). The area of these triangles will add up to |xbasexheight(of 
a small triangle) which is \ x 2-rrr x a = irra 



Step 3 : Calculate a 

a can be calculated by using the Theorem of Pythagoras. Therefore: 

a = v r 2 + h 2 



Step 4 : Calculate the area of the circular base 



Ah = irr 



Step 5 : Calculate the area of the curved walls 



Step 6 : Calculate surface area A 



irryr 2 + h 2 



irr + irryr 2 + h 2 



12S 



CHAPTER 76. GEOMETRY 



16.2 



Volume of a Pyramid: The volume of a pyramid is found by: 

V= l -A.k 

where A is the area of the base and h is the perpendicular height. 
A cone is like a pyramid, so the volume of a cone is given by: 

V = —irr h. 



A square pyramid has volume 



V=\a\ 



where a is the side length of the square base. 

© See video: VMfqj at www.everythingmaths.co.za 



Example 2: Volume of a Pyramid 



QUESTION 


What is the volume of a square pyramid, 3 cm high with a side length of 2 cm? 




SOLUTION 




Step 1 : Determine the correct formula 




The volume of a pyramid is 




V = -A.h, 
3 




where A is the area of the base and h is the height of the pyramid. 


For a square 


base this means 

V = —a .a .h 






where a is the length of the side c 


)f the square base. 




/3 cm 1 






^^ 






2 cm \ 


/2 cm 





129 



16.2 



CHAPTER 16. GEOMETRY 



Step 2 : Substitute the given values 



.2.2.3 



4 cm 



.12 



We accept the following formulae for volume and surface area of a sphere (ball). 



Surface area 
Volume 



47rr 
4 



Exercise 16-1 



1 . Calculate the volumes and surface areas of the following solids: (Hint for (e): find the perpen- 
dicular height using Pythagoras). 




d sphere 



2. Water covers approximately 71% of the Earth's surface. Taking the radius of the Earth to be 6378 
km, what is the total area of land (area not covered by water)? 



130 



CHAPTER 76. GEOMETRY 



16.3 



3. 



A triangular pyramid is placed on top of a triangular 
prism. The prism has an equilateral triangle of side 
length 20 cm as a base, and has a height of 42 cm. 
The pyramid has a height of 12 cm. 

(a) Find the total volume of the object. 

(b) Find the area of each face of the pyramid. 

(c) Find the total surface area of the object. 




I\n More practice f ►) video solutions Of) or help at www.everythingmaths.co.z 



(1.)012u (2.)012v (3.)012w 




16.3 Similarity of Polygons 



In order for two polygons to be similar the following must be true: 



1 . All corresponding angles must be congruent. 



2. All corresponding sides must be in the same proportion to each other. Refer to the picture below: 
this means that the ratio of side AE on the large polygon to the side PT on the small polygon 
must be the same as the ratio of side AB to side PQ, BC/QR etc. for all the sides. 




1 . A = P; B 
E = f 
and 



};C = R;D 



p AB_ _ BC_ _ CD _ DE _ E_A 
Z ' PQ ~ QR ~ RS ~ ST ~ TP 

then the polygons ABCDE and 
PQRST are similar. 



131 



16.3 



CHAPTER 16. GEOMETRY 



Example 3: Similarity of Polygons 



QUESTION 



Polygons PQTU and PRSU are sim- 
ilar. Find the value of x. 



Polygons PQTU and PRSU are sim- 
ilar. Find the value of x. p 




SOLUTION 



Step 1 : Identify corresponding sides 

Since the polygons are similar, 



PQ 
PR 


= 


TU 

su 


X 


= 


3 


x + (3 — x) 


4 


X 

'• 3 


= 


3 

4 


.'. x 


= 


9 
4 



132 



CHAPTER 76. GEOMETRY 



16.4 




16.4 Triangle Geometry 





Two line segments are divided in the same proportion if the ratios between their parts are equal. 

AB _ x _ kx _ DE 
~BC ~ y ~ ky ~ ~EF 

.-. the line segments are in the same proportion 




If the line segments are proportional, the following also hold: 



CB _ FE 



AC DF 

2. AC .FE = CB .DF 



r> AB_ _ DEI and ^- — -^ 

J - BC FE AB DE 



4 AB_ _ DK , nf J AC_ _ D_F 
AC DF AB DE 



Proportionality of triangles 

Triangles with equal heights have areas which are in the same proportion to each other as the bases of 
the triangles. 



hi = 


h 2 




area AABC 


\BC x hi 


BC 


' ' area ADEF 


\EF x h 2 


EF 


A 


D 


_Ss 




133 



76.4 



CHAPTER 16. GEOMETRY 



A special case of this happens when the bases of the triangles are equal: 
Triangles with equal bases between the same parallel lines have the same area. 



area AABC = - .h.BC = area ADBC 
2 




Triangles on the same side of the same base, with equal areas, lie between parallel lines. 

If area AABC = area ABDC 
then AD II BC 




Theorem 1. Proportion Theorem: A line drawn parallel to one side of a triangle divides the other two 
sides proportionally. 




Given:AABC with line DE \\ BC 
R.T.P.: 



AD _ AE 
~DB ~ ~EC 



Proof: Draw hi from E perpendicular to AD, and hi from D perpendicular to AE. 



134 



CHAPTER 16. GEOMETRY 



16.4 



Draw BE and CD. 



area AADE 
area ABDE 

area A^£>£ 

area AC ED 

but area ABDE 

area AADE 

" area ABDE 

AD 

' ' DB 

Di? divides AB and AC proportionally. 



\AD.hi AD 



\DB.h x DB 

\AE.h 2 _ AE 

\EC.hi ~ EC 

area ACED (equal base and height) 

area AADE 

area ACED 

AE 

EC 



Similarly, 



AD 
AB 
AB 


AE 
AC 
AC 


BD 


CE 



Following from Theorem 1, we can prove the midpoint theorem. 

Theorem 2. Midpoint Theorem: A line joining the midpoints of two sides of a triangle is parallel to 
the third side and equal to half the length of the third side. 

Proof: 

This is a special case of the Proportionality Theorem (Theorem 1). 

A 

If AB = BD and AC = AE, 

and 

AD = AB + BD = 2AB 

AE = AC + CB = 2AC 

then DE II BC and BC = 2DE. 



Theorem 3. Similarity Theorem 1: Equiangular triangles have their sides in proportion and are there- 
fore similar. 






G\\en:AABC and ADEF with A = D; B = E; C = F 
R.T.P.: 



AB 
L>E 



AC 
DF 



Construct: G on AB, so that AG = DE 
H on AC, so that AH = DF 



l.V> 



76.4 



CHAPTER 16. GEOMETRY 



Tip 



Proof: In A's AGH and DEF 

AG = DE;AH = DF 

A = D 
:. AAGH = ADEF 
.-. AGH = E = B 
:. GH || BC 

AG _ AH 
•'■ AB ~ AC 

DE _ DF 
•'■ ~AB ~ AC 
:. AABC HI ADEF 



(constant) 
(given) 
(SAS) 

(corresponding Z's equal) 
(proportion theorem) 

(AG = DE; AH = DF) 



means "is similar to" 



Theorem 4. Similarity Theorem 2: Triangles with sides in proportion are equiangular and therefore 
similar. 




Given-.AABC with line DE such that 



R.T.P.: DE || BC; AADE ||| AABC 
Proof: 



AD _ AE 
~DB ~ ~EC 



Draw hi from E perpendicular to AD, and h 2 from D perpendicular to AE. 
Draw BE and CD. 



area AADE 
area ABDE 

area AADE 
area ACED 
AD 
~DB 
area AADE 
area ABDE 
. area ABDE 



\AD.hy AD 



but 



\DB.hi DB 
\AE.h 2 _ AE 
\EC.bv ~ EC 

AE , ■ \ 
EC <g ' Ven) 
area AADE 
area ACED 
area ACED 



.•. DE || BC (same side of equal base DE, same area) 

.-. ADE = ABC (corresponding Z's) 
and AED = ACB 

.-. AADE and AABC are equiangular 

.-.AADE HI AABC (AAA) 

Theorem 5. Pythagoras' Theorem: The square on the hypotenuse of a right angled triangle is equal to 
the sum of the squares on the other two sides. 



i:«i 



CHAPTER 16. GEOMETRY 



16.4 



Given:AABC with A = 90° 




2 _ a c>2 , Ar a 



R.T.P.: BC 2 = AB 2 + AC 



Proof: 



LetC 


= 


X 


DiC" 


= 


90° -x (Z'sofa A) 


DAB 


= 


X 


ABD 


= 


90° -i (Z'sofa A) 


BDA 


= 


CD A = A = 90° 



. AABD|||AC,BAand ACAD|||AC.BA (AAA) 



AB _ BD _ ( AD\ ,CA_CD_ f AD 
CB ~ ~BA ~ \CA J an C~B~'CA~\BA 



.-. AS 2 = CB x BD and AC* 2 =CB xCD 



i.e. BC* 2 



CB(BD + CD) 

CB(CB) 

CB 2 

AB 2 + AC 2 



l.'J7 



76.4 



CHAPTER 16. GEOMETRY 



Example 4: Triangle Geometry 7 



QUESTION 



In AGHI, GH \\ LJ; GJ || LK and j§ = |. Determine §f 



SOLUTION 




Step 1 : Identify similar triangles 



LIJ = GIH 
JLI = HGI 
.-.ALU HI AGIH 



(Corresponding Z's) 
(Equiangular A's) 



LIK = GIJ 

KLI = JGI 

.ALIK HI AGIJ 



(Corresponding Z's) 
(Equiangular A's) 



Step 2 : Use proportional sides 



and 



HJ _ GL 

IT ~ TT 

GL _ JK 

TT ~ ~kI 

_ 5 

~ 3 

HJ _ 5 

77 ~ 3 



(ALU HI AGIH) 
{ALIK HI AGIJ) 



Step 3 : Rearrange to find the required ratio 



HJ 
KI 



HJ JI 
J I X KI 



i:',s 



CHAPTER 16. GEOMETRY 



16.4 



We need to calculate j^\ We were given j^ = | So rearranging, we have 



JK = %KI And: 



JI 



JI 
KI 



KI 
KI + KI 

KI 



Using this relation: 



JK 

5 

3 

8 

3 

8 

3 



5 8 
3 X 3 



40 



Example 5: Triangle Geometry 2 



QUESTION 



PQRS is a trapezium, with PQ || RS. 
Prove that PT.TR = ST. TQ. 




SOLUTION 



Step 4 : Identify similar triangles 



Pi = 5! 

Qi = Ri 
APTQ HI ASTR 



(alternate Z's) 
(alternate Z's) 
(equiangular A's) 



Step 5 : Use proportional sides 



PT ST 

TQ TR 

,PT.TR = ST .TQ 



(APTQ\\\ASTR) 



139 



76.4 



CHAPTER 16. GEOMETRY 



Exercise 16-2 



1 . Calculate SV 




2 UB_ = 3 pj d OS 
*■' YB 2 SB ' 




3. Given the following figure with the following lengths, find AE, EC and BE. 
BC = 15 cm, AB = 4 cm, CD = 18 cm, and ED = 9 cm. 




4. Using the following figure and lengths, find I J and KJ. 
HI = 26 m, KL = 13 m, JL = 9 m and HJ = 32 m. 




140 



CHAPTER 76. GEOMETRY 



16.4 



5. Find FH in the following figure. 




6. BF = 25 m, AB = 13 m, AD = 9 m, DF = 18 m. 

Calculate the lengths of BC, CF, CD, CE and EF, and find the ratio 




7. If LAI || JK, calculate y. 




A"j More practice (►) video solutions (9) or help at www.everythingmaths.co.za 



(1.)012x (2.)012y (3.)012z (4.) 0130 (5.) 0131 (6.) 0132 
(7.) 0133 



111 



76.5 



CHAPTER 16. GEOMETRY 




16.5 Co-ordinate Geometry 




Equation of a Line Between Two Points 



EMBCL 



See video: VMftf at www.everythingmaths.co.za 

There are many different methods of specifying the requirements for determining the equation of a 
straight line. One option is to find the equation of a straight line, when two points are given. 

Assume that the two points are {xi;yi) and (x 2 ; 3/2), and we know that the general form of the equation 
for a straight line is: 



y = mx + c 



(16.1) 



Tip 


If you are 
culate the 
line passin 
points, use 


asked to cal- 
equation of a 
g through two 


m = 


2/2 - 2/1 
X 2 — Xl 


to calculate m and then 


use: 




y-vi = 


= m(x — an) 


to determ 
tion. 


ne the equa- 



So, to determine the equation of the line passing through our two points, we need to determine values 
for m (the gradient of the line) and c (the y-intercept of the line). The resulting equation is 



y — j/i = m(w - an) 



where (an; 2/1) are the co-ordinates of either given point. 



Extension: 



Finding the second equation for a straight line 



This is an example of a set of simultaneous equations, because we can write: 

j/i = mil + c 
y 2 = mx 2 + c 

We now have two equations, with two unknowns, m and c. 



(16.2) 



(16.3) 
(16.4) 



mi2 — 771x1 


(16.5) 


2/2 -7/1 
X 2 — Xl 


(16.6) 


<mx\ + c 


(16.7) 


7/1 - 777X1 


(16.8) 



Subtract (16.3) from (16.4) y 2 —y\ = mx 2 — man 



Re-arrange (1 6.3) to obtain c j/i 



Now, to make things a bit easier to remember, substitute (16.7) into (16.1): 

y = mx + c (16.9) 

= mx + (7/1 — mil) (16.10) 

which can be re-arranged to: y — yi = m(x — an) (16.11) 



For example, the equation of the straight line passing through (— 1; 1) and (2; 2) is given by first calcu- 



142 



CHAPTER 16. GEOMETRY 



16.5 



latingm 



2/2 


-yi 


X'2 


- Xl 


2 


- 1 


2- 


(-1) 


1 




3 





and then substituting this value into 



to obtain 



Then substitute ( — 1: 1) to obtain 



y -yi = m(x - xi) 



y-yi = ^(x-xi). 



V-W = 3^-(-l)) 

1 1 
v-i = ^+3 

1 1 , 

y = -x H hi 

y 3 3 

1 4 

v = r + s 



So, y = |x + | passes through (— 1; 1) and (2; 2). 




Figure 1 6.2: The equation of the line passing through (— 1; 1) and (2; 2) is y = \x + f . 



Example 6: Equation of Straight Line 



QUESTION 



Find the equation of the straight line passing through (—3; 2) and (5; 8). 



143 



76.5 CHAPTER 16. GEOMETRY 



SOLUTION 


Step 1 : Label the points 




(xi;yi) 


= M; 2) 


(a&;ife) 


= (5; 8) 


Step 2 : Calculate the gradient 




m = 


2/2 -J/i 

X2 — Xl 




8-2 




5 -(-3) 


= 


6 
5 + 3 


= 


6 
8 


= 


3 

4 


Step 3 : Determine the equation of the line 


V-Vi = 


mix — x±) 


y-m = 


|(*-(-3)) 


y = 


|(* + 3) + 2 


= 


iL+f.3 + 2 

4 4 


= 


3 9 8 

7^+7 + 7 

4 4 4 


= 


3 17 

4 4 


Step 4 : Write the final answer 




The equation of the straight line that passes through (—3; 2) and (5; 8) is y = 

jx+i[. 

4 ' 4 





Equation of a Line Through One Point and membcm 
Parallel or Perpendicular to Another Line 



Another method of determining the equation of a straight-line is to be given one point, (wi;yi), and to 
be told that the line is parallel or perpendicular to another line. If the equation of the unknown line is 



144 



CHAPTER 76. GEOMETRY 



16.5 



y = mx + c and the equation of the second line is y = m x + c , then we know the following: 



If the lines are parallel, then m = m Q 

If the lines are perpendicular, then m x m = — 1 



(16.12) 
(16.13) 



Once we have determined a value for m, we can then use the given point together with: 

y — yi = m(x - xi) 
to determine the equation of the line. 
For example, find the equation of the line that is parallel toy = 2x — 1 and that passes through (— 1; 1). 

First we determine m, the slope of the line we are trying to find. Since the line we are looking for is 
parallel to y = 2x — 1, 

m = 2 

The equation is found by substituting m and ( — 1; 1) into: 



y- 


in 


= 


m(x — xi) 


y 


-l 


= 


2(x-(-l) 


y 


-l 


= 


2(z + l) 


y 


-l 


= 


2z + 2 




y 


= 


2x + 2 + 1 




y 


= 


2x + 3 




Figure 16.3: The equation of the line passing through (—1; 1) and parallel toy = 2x — 1 is y = 2x+3. It 
can be seen that the lines are parallel to each other. You can test this by using your ruler and measuring 
the perpendicular distance between the lines at different points. 



Inclination of a Line 



EMBCN 



In Figure 16.4(a), we see that the line makes an angle 9 with the x-axis. This angle is known as the 
inclination of the line and it is sometimes interesting to know what the value of d is. 



115 



76.5 



CHAPTER 16. GEOMETRY 




(a) 



. 


. 


/ f(x) = Ax - 


-4 




3 - 




/ f 
/ / 
/ / 






2 - 




/ /g(x) = 2x- 
1 l 


-2 




1 - 




"l 1 J t 






■ 




1 

2 3 


1 





(b) 



Figure 1 6.4: (a) A line makes an angle 9 with the x-axis. (b) The angle is dependent on the gradient. If 
the gradient of/ is m s and the gradient of g is m g then m/ > m 9 and 0/ > 6 g . 



Firstly, we note that if the gradient changes, then the value of 6 changes (Figure 1 6.4(b)), so we suspect 
that the inclination of a line is related to the gradient. We know that the gradient is a ratio of a change 
in the j/-direction to a change in the x-direction. 



±1 
Ax 



But, in Figure 16.4(a) we see that 



tan£ 



±1 
Ax 
tan 6 



For example, to find the inclination of the line y = x, we know m = 1 



. tan 8 



1 

45° 



Exercise 16-3 



1 . Find the equations of the following lines 

(a) through points (— 1;3) and (1;4) 

(b) through points (7; -3) and (0;4) 

(c) parallel toy = \x + 3 passing through (— 1; 3) 

(d) perpendicular to y = — \x + 3 passing through (—1; 2) 

(e) perpendicular to 2y + x = 6 passing through the origin 

2. Find the inclination of the following lines 

(a) y = 2x - 3 

(b) y = \x - 7 

(c) Ay = 3x + 8 

(d) y = — |x + 3 (Hint: if m is negative 9 must be in the second quadrant) 

(e) Zy + x - 3 = 

3. Show that the line y = k for any constant k is parallel to the x-axis. (Hint: Show that the 
inclination of this line is 0°.) 



146 



CHAPTER 76. GEOMETRY 



16.6 



4. Show that the line x = k for any constant k is parallel to the y-axis. (Hint: Show that the 
inclination of this line is 90°.) 



Aj More practice f ►) video solutions ([J or help at www.everythingmaths.< 



(1.) 0134 (2.) 0135 (3.) 0136 (4.) 0137 




16.6 Transformations 




EMBCO 



Rotation of a Point 



EMBCP 



When something is moved around a fixed point, we say that it is rotated about the point. What happens 
to the coordinates of a point that is rotated by 90° or 180° around the origin? 



Activity: 



Rotation of a Point by 90° 



Complete the table, by filling in the coordinates of the points shown in the figure. 



Point 


x-coordinate 


^-coordinate 


A 






B 






C 






D 






E 






F 






G 






H 







, C| 1 







What do you notice about the x-coordinates? What do you notice about the ^-coordinates? 

What would happen to the coordinates of point A, if it was rotated to the position of point C? 

What about if point B rotated to the position of D? 



Activity. 



Rotation of a Point by 180° 



I 



Complete the table, by filling in the coordinates of the points shown in the figure. 



147 



76.6 



CHAPTER 16. GEOMETRY 



Point 


^-coordinate 


^/-coordinate 


A 






B 






C 






D 






E 






F 






G 






H 







-F 








^ ~ 


■■£ j%>yFi 


-tl 7^ 


, " ' \\\ 


c ; Y \\\ A 


< A ' i 


T / T 


' / 


\ / M- 


X- m *, P 


--*--?-~^---- 










i ■ j_ j_ 



What do you notice about the x-coordinates? What do you notice about the ^-coordinates? 

What would happen to the coordinates of point A, if it was rotated to the position of point P? 

What about point F rotated to the position of Bl 



From these activities you should have come to the following conclusions: 



90° clockwise rotation: 

The image of a point P(x;y) rotated clockwise 
through 90° around the origin is P'(y; —x). 
We write the rotation as (a;; y) — > (y; —x). 











y 
















J>(* 


y) 
















/ 




\ 




\ 


\ 










/ 
1 




\ 






\ 


f'fa 


;-x) 




1 






\ 


j. 


i-- 


«- 


1 






\ 














i 


:r 






\ 










/ 










\ 


s. 






















"^ 































90° anticlockwise rotation: 
The image of a point P(x\y) rotated anticlockwise 
through 90° around the origin is P'(— y;x). 
We write the rotation as (x;y) — > (—y;x). 



180° rotation: 

The image of a point P(x; y) rotated through 180° 

around the origin is P'(— x; —y). 

We write the rotation as (x; y) — > (—x; —y). 















y 


















P(x 


y) 
















/ 


s 


\ 
















/ 




\ 






\ 








I 




I 


h 








\ 






-y 


~\ 


V* 


J- 


-J* 








1 


.!' 


p.. 




\ 










/ 












\ 


-. 






s 


• 
































V 












P(x 


y) 
















/ 


s 


\ 
















( 




\ 






\ 








I 




( 


A 








\ 






\ 




\ 


V 


r 






1 
/ 


X 












\ 




/ 
















\ 


i " 


• 
















-■'" 




-u) 







Exercise 16-4 



1 . For each of the following rotations about the origin: 
(i) Write down the rule. 
(ii) Draw a diagram showing the direction of rotation. 

(a) OA is rotated to OA' with A(4; 2) and A'(-2; 4) 

(b) OB is rotated to OB' with B(-2; 5) and B'(5; 2) 



lis 



CHAPTER 76. GEOMETRY 



16.6 



(c) OC is rotated to OC with C(-l; -4) and C"(l;4) 
2. Copy AXFZ onto squared paper. The co-ordinates are given on the picture. 

(a) Rotate AXYZ anti-clockwise through an angle of 90° about the origin to give AX'Y'Z' . 
Give the co-ordinates of X' , Y' and Z' . 

(b) Rotate AXYZ through 180° about the origin to give AX"Y"Z". Give the co-ordinates of 
X", y"and Z". 





















X( 


i; 4) 














































































































z(- 


4;- 


lK 
































































1 


'(-1 


;-4) 











A" 1 ) More practice f ►) video solutions fyj or help at www.everythingmaths.co.za 



(1.) 0138 (2.) 0139 




When something is made larger, we say that it is enlarged. What happens to the coordinates of a 
polygon that is enlarged by a factor fc? 



Activity: 



Enlargement of a Polygon 






Complete the table, by filling in the coordinates of the points shown in the figure. Assume 
each small square on the plot is 1 unit. 



149 



76.6 



CHAPTER 16. GEOMETRY 



Point 


^-coordinate 


^/-coordinate 


A 






B 






C 






D 






E 






F 






G 






H 







1 1 1 






' i — r n — r 




. 




ih 
































E 






























A 






















































: < 






-4 


" 7-1 ' 




r? 






























TVt 






H 



































What do you notice about the x-coordinates? What do you notice about the ^-coordinates? 
What would happen to the coordinates of point A, if the square ABCD was enlarged by a 

factor of 2? 



Activity: 



Enlargement of a Polygon 













I' 
































H 1 
















1 










H 






\ A" 




,, 




















. ■' \K 
1 




••-~~ J 











In the figure quadrilateral HIJK has been enlarged by a factor of 2 through the origin to be- 
come H'I'J'K'. Complete the following table using the information in the figure. 



Co-ordinate 


Co-ordinate' 


Length 


Length' 


H = (;) 


#'-(;) 


OH = 


OH' = 


/ = (;) 


/' = (;) 


OI = 


OI' = 


J = (;) 


J' = ( ; ) 


OJ = 


OJ' = 


K = ( ; ) 


A" = ( ; ) 


OK = 


OK' = 



What conclusions can you draw about 

1. the co-ordinates 

2. the lengths when we enlarge by a factor of 2? 



We conclude as follows: 

Let the vertices of a triangle have co-ordinates S(xi)yi), T(x 2 : jfe), U{x- i :y: i ). AS'T'U' is an enlarge- 
ment through the origin of ASTU by a factor of c (c > 0). 

• ASTU is a reduction of AS'T'U' by a factor of c. 

• AS'T'U' can alternatively be seen as an reduction through the origin of ASTU by a factor of 
\. (Note that a reduction by | is the same as an enlargement by c). 

• The vertices of AS'T'U' are S'(cxi;cyi), T'icxi^cyi), U'{cx3,cy?,). 



150 



CHAPTER 76. GEOMETRY 



76.6 



The distances from the origin are OS' = (c . OS), OT' = (c . OT) and OU' = (c . OU). 

9 











































SJt' 


























































,S" 


















T 




























lEl~- " 










s. -s 


fu^, - 



































12 3 4 5 6 7 



9 10 11 



Chapter 16 



End of Chapter Exercises 



1 . Copy polygon STUV onto squared paper and then answer the following questions. 

3 







2 






s 










1 




/ ^\ 




T 



















-3 


-2 


-1 









l/ 


4 








-1 






















V*^^^ 












-2 






























u 










-3 















(a) What are the co-ordinates of polygon STUV1 

(b) Enlarge the polygon through the origin by a constant factor of c = 2. Draw this 
on the same grid. Label it S'T'U'V. 



151 



76.6 



CHAPTER 16. GEOMETRY 



(c) What are the co-ordinates of the vertices of S'T'U'V'?. 
2. AABC is an enlargement of AA'B'C by a constant factor of k through the origin. 

5 







A 




4 




















3 


















A' 


2 










B 
















B' y 
























-5 


-4 / 


-3 


-2 j 


-1 






2 


3 


4 








-2 
















C" 




-3 




















-4 












C 








-5 













(a) What are the co-ordinates of the vertices of AABC and AA'B'C'? 

(b) Giving reasons, calculate the value of k. 

(c) If the area of AABC is m times the area of AA'B'C", what is m? 
3. Examine the polygon below. 





4 








M 






3 














2 










AT 




P 
1 











Q 










-2 


-1 

-1 





i 


2 


3 


4 




-2 













(a) What are the co-ordinates of the vertices of polygon MNPQ1 

(b) Enlarge the polygon through the origin by using a constant factor of c = 3, 
obtaining polygon M'N'P'Q' . Draw this on the same set of axes. 



152 



CHAPTER 16. GEOMETRY 16.6 



(c) What are the co-ordinates of the new vertices? 

(d) Now draw M"N"P"Q" which is an anticlockwise rotation of MNPQ by 90° 
around the origin. 

(e) Find the inclination of OM" . 



A -1 ) More practice \wj video solutions ({J or help at www.everythingmaths.i 
(1.)01zi (2.)01zj (3.) 01zk 



153 



Trigonometry 





17.1 Introduction 




Building on Grade 10 Trigonometry, we will look at more general forms of the the basic trigonometric 
functions next. We will use graphs and algebra to analyse the properties of these functions. We will 
also see that different trigonometric functions are closely related through a number of mathematical 
identities. 

© See introductory video: VMfva at www.everythingmaths.co.za 





17.2 Graphs of Trigonometric 
Functions 



Functions of the Form y = sin(k6) 



EMBCT 



In the equation, y = sm(kd), k is a constant and has different effects on the graph of the function. 
The general shape of the graph of functions of this form is shown in Figure 17.1 for the function 
f(9) = sm(29). 




Figure 17.1: Graph of /(#) = sm(29) (solid line) and the graph of g{8) = sin(#) (dotted line). 



Exercise 17-1 



On the same set of axes, plot the following graphs: 

1. a(0) = sin 0,56» 

2. 6(0) = sin Id 

3. c{9) = sin 1,56* 



154 



CHAPTER 17. TRIGONOMETRY 



17.2 



4. d(6) = sin 29 

5. e(0) = sin 2,50 

Use your results to deduce the effect of k. 



A 4 ) More practice f ►) video solutions (?) or help at www.everythingmaths.co.za 



(1.) 013c 

You should have found that the value of k affects the period or frequency of the graph. Notice that in 
the case of the sine graph, the period (length of one wave) is given by ^-, 

These different properties are summarised in Table 1 7.1 . 



Table 17.1: Table summarising general shapes and positions of graphs of functions of the form 
y = sin(fc:r). The curve y = sin(x) is shown as a dotted line. 



k >0 






k<0 






Domain and Range 

For f(9) = sm(kd), the domain is {9 : 9 £ IR} because there is no value of 8 e M for which f(9) is 
undefined. 

The range of f(9) = sin(fc6») is {/(0) : f(9) e [-1; 1]}. 



Intercepts 

For functions of the form, y = sm(k9), the details of calculating the intercepts with the y axis are 
given. 

There are many x-intercepts. 

The j/-intercept is calculated by setting 9 = 0: 

y = s'm(k9) 
yint = sin(O) 
= 



155 



77.2 



CHAPTER 17. TRIGONOMETRY 



Functions of the Form y = cos(kO 



EMBCU 



In the equation, y = cos(k9), k is a constant and has different effects on the graph of the function. 
The general shape of the graph of functions of this form is shown in Figure 17.2 for the function 
f(9) = cos(20). 




Figure 1 7.2: Graph of f(9) = cos(26>) (solid line) and the graph of g(9) = cos(d) (dotted line). 



Exercise 17-2 



On the same set of axes, plot the following graphs: 

1. a{9) = cos 0,59 

2. b(0) = cos 16) 

3. c(9) = cos 1,56* 

4. d(0) = cos 28 

5. e(0) = cos 2,56* 

Use your results to deduce the effect of k. 

(/V 1 ) More practice (►) video solutions (9) or help at www.everythingmaths.co.za 

(1.) 01 3h 

You should have found that the value of k affects the period or frequency of the graph. The period of 
the cosine graph is given by ^jf-. 

These different properties are summarised in Table 1 7.2. 

Domain and Range 

For f(9) = cos(kd), the domain is {6 : 9 e R} because there is no value of 9 e R for which f(9) is 
undefined. 

The range of f(6) = cos{k9) is {/(<9) : f(6) e [-1; 1]}. 



15(i 



CHAPTER 17. TRIGONOMETRY 



17.2 



Table 17.2: Table summarising general shapes and positions of graphs of functions of the form 
y = cos(kx). The curve y = cos(:r) is plotted with a dotted line. 



k >0 


k < 


t 


i , 


' ' 


■ ' 



Intercepts 

For functions of the form, y = cos(kd), the details of calculating the intercepts with the y axis are 
given. 

The y-intercept is calculated as follows: 

y = cos(k8) 
Vint = cos(O) 
= 1 



Functions of the Form y = tan(/c6>) 



EMBCV 



In the equation, y = tan(kd), k is a constant and has different effects on the graph of the function. 
The general shape of the graph of functions of this form is shown in Figure 17.3 for the function 
f{8) = tan(20). 



[H/X 


pjib : 


yfr |Jy|* p y -p - 
I I I I I 


|/90/]/l80 j/270. |/360 
- |t y fr |t y fr 



Figure 17.3: The graph of /(0) = tan(26*) (solid line) and the graph of g{8) = tan(S) (dotted line). 
The asymptotes are shown as dashed lines. 



Exercise 17-3 



On the same set of axes, plot the following graphs: 
1. a{8) = tan 0,58 



157 



77.2 



CHAPTER 17. TRIGONOMETRY 



2. b(6) = tan 16) 

3. c(0) = tan 1,56 

4. d(0) = tan 26 

5. e(0) = tan 2,56 

Use your results to deduce the effect of fc. 



A" 1 ) More practice CrJ video solutions f?J or help at www.everythingmaths 



(1.) 01 3n 

You should have found that, once again, the value of k affects the periodicity (i.e. frequency) of the 
graph. As k increases, the graph is more tightly packed. As k decreases, the graph is more spread out. 
The period of the tan graph is given by ^-. 

These different properties are summarised in Table 1 7.3. 



Table 17.3: Table summarising general shapes and positions of graphs of functions of the form 

y = tan(kd). 



k > 


k < 




\J 


A 




f\ 






Y 



Domain and Range 

For f(9) = tan(fc0), the domain of one branch is {9 : 9 e (— 2£L; =^-)} because the function is 



undefined for 9 ■■ 



and ( 



k 



The range of f(9) = tan(fc0) is {f(9) : f(9) e (-oo; oo)}. 

Intercepts 

For functions of the form, y = tan(kd), the details of calculating the intercepts with the x and y axis 
are given. 

There are many x-intercepts; each one is halfway between the asymptotes. 

The i/-intercept is calculated as follows: 



V 


= 


tan(k9 


3/int 


= 


tan(O) 




= 






Asymptotes 

The graph of tanfc0 has asymptotes because as k9 approaches 90°, taafcfl approaches infinity. In other 
words, there is no defined value of the function at the asymptote values. 



1--.N 



CHAPTER 17. TRIGONOMETRY 



17.2 



Functions of the Form y = sin (6 + p) 



EMBCW 



In the equation, y = sin(0 + p), p is a constant and has different effects on the graph of the function. 
The general shape of the graph of functions of this form is shown in Figure 17.4 for the function 
/(0) = sin(0 + 3O°). 




Figure 1 7.4: Graph of /(0) = sin(0 + 30°) (solid line) and the graph of g(B) = sin(0) (dotted line). 



Exercise 17-4 



On the same set of axes, plot the following graphs: 

1. a(0) = sin(6» - 90°) 

2. 6(0) =sin(0-6O°) 

3. c(0) = sin0 

4. d{6) = sin(0 + 9O°) 

5. e(0) = sin(0 + 18O°) 

Use your results to deduce the effect of p. 

Q\+) More practice CrJ video solutions Cfj or help at www.everythingmaths.co.za 

(1.) 013t 

You should have found that the value of p affects the position of the graph along the j/-axis (i.e. the 
j/-intercept) and the position of the graph along the x-axis (i.e. the phase shift). The p value shifts the 
graph horizontally. If p is positive, the graph shifts left and if p is negative the graph shifts right. 

These different properties are summarised in Table 1 7.4. 

Domain and Range 

For /(0) = sin(0 + p), the domain is {0 : e R} because there is no value of € R for which /(0) is 
undefined. 

The range of /(0) = sin(0 + p) is {/(0) : f{6) e [-1; 1]}. 



159 



77.2 



CHAPTER 17. TRIGONOMETRY 



Table 17.4: Table summarising general shapes and positions of graphs of functions of the form 
y = sin(6< + p). The curve y = sin(0) is plotted with a dotted line. 



p>0 





T* 



p<0 





T* 



Intercepts 

For functions of the form, y = sin(9 + p), the details of calculating the intercept with the y axis are 
given. 

The i/-intercept is calculated as follows: set 9 = 0° 

y = sin(0 + p) 
Vint = sin(0 + p) 
= sin(p) 



Functions of the Form y = cos(6> + p 



EMBCX 



In the equation, y = cos(8 + p), p is a constant and has different effects on the graph of the function. 
The general shape of the graph of functions of this form is shown in Figure 17.5 for the function 
f{6) = cos(6> + 30°). 




Figure 17.5: Graph of f(8) = cos(9 + 30°) (solid line) and the graph of g(9) = cos(8) (dotted line). 



Exercise 17-5 



On the same set of axes, plot the following graphs: 

1. a(6) = cos(6»-90°) 

2. b{9) = cos(6>-60°) 

3. c(9) = cos9 

4. d{9) =cos(6» + 90°) 



160 



CHAPTER 17. TRIGONOMETRY 



17.2 



5. e(0) = cos(6» + 180°) 
Use your results to deduce the effect of p. 



f/Vj More practice (►) video solutions (9 J or help at www.everythingmaths.co.za 



(1.)013y 

You should have found that the value of p affects the j/-intercept and phase shift of the graph. As in the 
case of the sine graph, positive values of p shift the cosine graph left while negative p values shift the 
graph right. 

These different properties are summarised in Table 1 7.5. 



Table 17.5: Table summarising general shapes and positions of graphs of functions of the form 
y = cos(6 + p). The curve y = cosO is plotted with a dotted line. 



p>0 


p<0 


T /~\ 






f\ ^ 











Domain and Range 

For f{&) = cos(9 + p), the domain is {9 : 9 e M} because there is no value of 9 e E for which f(9) is 
undefined. 

The range of f(9) = cos(8 + p) is {/(0) : f(9) e [-1; 1]}. 



Intercepts 

For functions of the form, y = cos(9 + p), the details of calculating the intercept with the y axis are 
given. 

The j/-intercept is calculated as follows: set 9 = 0° 

y = cos(6 + p) 

Vint = COS(0 + p) 

= cos(p) 



Functions of the Form y = tan(6* +p) 



EMBCY 



In the equation, y = tan(# + p), p is a constant and has different effects on the graph of the function. 
The general shape of the graph of functions of this form is shown in Figure 17.6 for the function 
f{8) = tan(6» + 30°). 



161 



77.2 



CHAPTER 17. TRIGONOMETRY 




Figure 17.6: The graph of f(9) = tan(0 + 30°) (solid lines) and the graph of g{9) = tan(0) (dotted 
lines). 



Exercise 17-6 



On the same set of axes, plot the following graphs: 

1. a{9) = tan(0-9O°) 

2. 6(0) = tan(0-6O°) 

3. c(0) = tan0 

4. d(0) = tan(0 + 6O°) 

5. e(0) = tan(0 + 18O°) 

Use your results to deduce the effect of p. 



A"y More practice C ►) video solutions f9j or help at www.everythingmaths.co.za 



(1.) 0143 

You should have found that the value of p once again affects the y-intercept and phase shift of the 
graph. There is a horizontal shift to the left if p is positive and to the right if p is negative. 

These different properties are summarised in Table 17.6. 



Table 1 7.6: Table summarising general shapes and positions of graphs of functions of the form 
tan(0 + p). The curve y = tan(0) is plotted with a dotted line. 



k >0 


k< 




/ A 




A * 


/ V 




<i r 





Domain and Range 

For f(0) = tan(0 + p), the domain for one branch is {9 : G (—90° — p; 90° — p} because the function 
is undefined for 9 = —90° — p and 9 = 90° — p. 

The range of f(9) = tan((9 + p) is {/(0) : f(9) e (-oo;oo)}. 



ll>2 



CHAPTER 17. TRIGONOMETRY 



17.3 



Intercepts 

For functions of the form, y = tan(0 + p), the details of calculating the intercepts with the y axis are 
given. 



The j/-intercept is calculated as follows: set 9 = 0° 



y = tan(# + j 
Vint = tan(p) 



Asymptotes 

The graph of tan(# + p) has asymptotes because as 9 + p approaches 90°, tan(# + p) approaches 
infinity. Thus, there is no defined value of the function at the asymptote values. 



Exercise 17-7 



Using your knowledge of the effects of p and k draw a rough sketch of the following graphs without a 
table of values. 

1 . y = sin 3x 

2. y = — cos2z 

3. y = tan |x 

4. y = sin(x — 45°) 

5. y = cos(x + 45°) 

6. y = tan(x — 45°) 

7. y = 2 sin 2x 

8. y = sin(x + 30°) + l 

f/Vj More practice Cr) video solutions ("?) or help at www.everythingmaths.co.za 



(1.) 0148 (2.) 0149 (3.) 014a (4.) 014b (5.) 014c (6.) 014d 
(7.) 014e (8.) 014f 




17.3 Trigonometric Identities 



EMBCZ 



Deriving Values of Trigonometric Functions 
for 30°, 45° and 60° 



EMBDA 



Keeping in mind that trigonometric functions apply only to right-angled triangles, we can derive values 
of trigonometric functions for 30°, 45° and 60°. We shall start with 45° as this is the easiest. 



163 



17.3 



CHAPTER 17. TRIGONOMETRY 




Figure 1 7.7: An isosceles right angled triangle. 



Take any right-angled triangle with one angle 45°. Then, because one angle is 90°, the third angle is 
also 45°. So we have an isosceles right-angled triangle as shown in Figure 17.7. 

If the two equal sides are of length a, then the hypotenuse, h, can be calculated as: 

■ 2 2.2 

h = a + a 
= 2a 
:. h = V2a 

So, we have: 



sin(45°) 



opposite(45°) 
hypotenuse 



\/2a 
1 

V2 



cos(45°) 



adjacent(45°) 
hypotenuse 
a 

V2a 
1 

7i 



tan(45°) 



opposite(45°) 
adjacent(45°) 



We can try something similar for 30° and 60°. We start with an equilateral triangle and we bisect one 
angle as shown in Figure 1 7.8. This gives us the right-angled triangle that we need, with one angle of 
30° and one angle of 60°. 

If the equal sides are of length a, then the base is \a and the length of the vertical side, v, can be 
calculated as: 

1 



a — 


2 


2 

a — 


1 2 


3 2 

4° 




^3 





104 



CHAPTER 17. TRIGONOMETRY 



17.3 




Figure 17.8: An equilateral triangle with one angle bisected. 



So, we have: 

sin(30°) 



opposite(30°) 
hypotenuse 



sin(60°) 



cos (30°) 



tan(30°) 



adjacent(30°) 
hypotenuse 

2 " 

a 
73 
2 

opposite(30°) 
adjacent(30°) 



4a 



cos(60°) 



tan(60° 



opposite(60°) 
hypotenuse 

2 " 

a 

73 
2 



adjacent(60°) 
hypotenuse 



opposite(60°) 
adjacent(60°) 
V3„ 



1 
73 



73 



Tip 


Two useful tri 
remember 


angles to 


y 


>/60° 

1 


y^° 




73 




7 


/45° 


1 


/45° 






1 







You do not have to memorise these identities if you know how to work them out. 



Alternate Definition for tan 6 



EMBDB 



We know that tan 9 is defined as: 



tan( 



opposite 
adjacent 



This can be written as: 



opposite hypotenuse 
adjacent hypotenuse 
opposite hypotenuse 



But, we also know that sin 6 is defined as: 



hypotenuse adjacent 



opposite 



hypotenuse 



Kir, 



17.3 



CHAPTER 17. TRIGONOMETRY 



Tip 


tan 8 can 
fined as: 

tan 6 


also be de- 
sin e 
cos 6 



and that cos is defined as: 



Therefore, we can write 



adjacent 
hypotenuse 



tan( 



opposite hypotenuse 



hypotenuse adjacent 
sin x 

COSP 

sin# 
cos 6 



A Trigonometric Identity 



EMBDC 



One of the most useful results of the trigonometric functions is that they are related to each other. We 
have seen that tan 9 can be written in terms of sin 9 and cos 0. Similarly, we shall show that: 

sin + cos 9 = 1 
We shall start by considering AABC, 




We see that: 



and 



■ a AC 
Sm0= BC 

AB 
COS0= BC- 

We also know from the Theorem of Pythagoras that: 

AB 2 + AC 2 = BC 2 



So we can write: 



sm y + cos 



AC 2 AB 2 



BC 2 BC 2 
AC 2 + AB 2 



BC 2 



BC 2 
BC 2 



(from Pythagoras) 



166 



CHAPTER 17. TRIGONOMETRY 17.3 



Example 1: Trigonometric Identities A 



QUESTION 



Simplify using identities: 
1. tan 2 6». cos 2 # 



2. — Vs - tan 2 9 



SOLUTION 



Step 1 : Use known identities to replace tan 9 



tan 9 . cos 
sin' 



cos 2 9 
sin 9 



cos 9 



Step 2 : Use known identities to replace tan 9 

1 



— tan 
cos^ V 

1 sin 2 



cos^ y cos^ 
1 - sin 2 9 

cos 2 9 
cos 2 9 _ 



Example 2: Trigonometric Identities B 



QUESTION 



Prove: ^^^ = -£2£*_ 

cos x 1+sin x 



167 



17.3 



CHAPTER 17. TRIGONOMETRY 



SOLUTION 



LHS 



cos a; 
1 — sin x 1 + sin x 



cos x 1 + sin x 

1 — sin 2 x 



cosx(l + sinx) 

cos 2 x 
cosx(l + sinx) 
cosx 



RHS 



Exercise 17-8 



1 . Simplify the following using the fundamental trigonometric identities: 

/~\ cos 9 
(£ » tanfl 

(b) cos 2 6Uan 2 6» + tan 2 6. sin 2 6 

(c) 1 - tan 2 6. sin 2 6 

(d) l-sm9.cos6.ta.Ti6 

(e) 1 - sin 2 6 

lf\ J 1— cos 9 



2. Prove the following: 



(a) 



cos 8 1 — sin 

,2 



(b) sin 2 6 + (cos 6 - tan 6) (cos 6 + tan 6) = 1 - tan 2 



(c) 



(2 rus" 61-1) 



2-tan 2 ( 



(1+tan 2 9) 1+tan 2 9 



(e) 



cose 

2 sin 9 cos 



Sill V + COS t 



tf> (iff + tan6) ) - cosf 



l/V) More practice \w\ video solutions f?) or help at www.everythingmaths.c 



(1.)014g (2.) 014h 



IliN 



CHAPTER 17. TRIGONOMETRY 



17.3 



Reduction Formula 



EMBDD 



Any trigonometric function whose argument is 90° ±9; 180° ±9; 270° ±9 and 360° ±9 (hence —9) can 
be written simply in terms of 9. For example, you may have noticed that the cosine graph is identical 
to the sine graph except for a phase shift of 90°. From this we may expect that sin(90° + 9) = cos 9. 



Function Values of 180° ± ( 



Activity: 



Reduction Formulae for Function Values of 180° ± 9 



1 . Function Values of (180° 9) 

(a) In the figure P and P' lie on the cir- 
cle with radius 2. OP makes an angle 
9 = 30° with the x-axis. P thus has coor- 
dinates (V3; 1). If P' is the reflection of 
P about the j/-axis (or the linex = 0), use 
symmetry to write down the coordinates 
ofP'. 



(b) Write down values for sin 6 
tan 9. 



and 




(c) Using the coordinates for P' deter- 
mine sin(180° - 9), cos(180° - 9) and 
tan(180° -6). 

(d) From your results try and determine a relationship between the function values 
of (180° - 0) and 9. 

2. Function values of (180° +9) 



(a) In the figure P and P' lie on the cir- 
cle with radius 2. OP makes an angle 
9 = 30° with the x-axis. P thus has coor- 
dinates (\/3; 1). P' is the inversion of P 
through the origin (reflection about both 
the x- and y-axes) and lies at an angle of 
180° + 9 with the x-axis. Write down the 
coordinates of P' . 



(b) Using the coordinates for P' 
mine sin(180° + 9), cos(180 D + 
tan(180°+6>). 



(c) From your results try and determine a re- 
lationship between the function values of 
(180° +9) and (9. 




169 



17.3 



CHAPTER 17. TRIGONOMETRY 



Activity: 



Reduction Formulae for Function Values of 360° ± 9 



1 . Function values of (360° — 9) 

(a) In the figure P and P' lie on the cir- 
cle with radius 2. OP makes an angle 
9 = 30° with the x-axis. P thus has coor- 
dinates (V3; 1). P' is the reflection of P 
about the z-axis or the line y = 0. Using 
symmetry, write down the coordinates of 
P'. 

(b) Using the coordinates for P' deter- 
mine sin(360° - 0), cos(360° - 9) and 
tan(360° - 9). 

(c) From your results try and determine a re- 
lationship between the function values of 
(360° - 9) and 9. 




It is possible to have an angle which is larger than 360°. The angle completes one revolution to give 
360° and then continues to give the required angle. We get the following results: 

sin(36O o + 0) = sin 6» 
cos(360° + 6>) = cos9 
tan(36O o + 0) = tan0 

Note also, that if k is any integer, then 



sin(/c360° + 9) -. 


= sin( 


cos(fe360 D + 9) -- 


= cos 


tan(fe360° + 9) -. 


= tan 



Example 3: Basic Use of a Reduction Formula 



QUESTION 


Write sin 293° as th 
SOLUTION 


e function of an acute angle 












We note that 293° 
where we used the 


= 360° - 
fact that 


67° thus 
sin 293° 

sin(360° - 


0) 


= sin(360° - 67 c 
= —sin 67° 

= — sin#. Check, 


) 
usir 


g your calct 


lator, that these 



170 



CHAPTER 17. TRIGONOMETRY 



17.3 



values are in fact equal: 



sin 293° = -0,92. 
-sin 67° = -0,92. 



Example 4: More Complicated 



QUESTION 



Evaluate without using a calculator: 

tan 2 210° - (1 + cos 120°) sin 2 225° 



SOLUTION 



tan 210° - (1 + cos 120°) sin 225° 

[tan(180° + 30°)] 2 - [1 + cos(180° - 60°)] . [sin(180° + 45°)] 2 

(tan30°) 2 - [1 + (-cos60°)].(-sin45°) 2 



1 

--(- 

3 V 2 

1 1 
3 ~ 4 " 



1- - 



1 
2 

1 

12 



1 



Exercise 17-9 



1 . Write these equations as a function of 9 only: 

(a) sin(180° - 9) 

(b) cos(180° - 9) 

(c) cos(360° - 9) 

(d) cos(360° + 9) 

(e) tan(180° - 9) 

(f) cos(360° + 9) 

2. Write the following trig functions as a function of an acute angle: 



171 



17.3 CHAPTER 17. TRIGONOMETRY 



(a) sin 163° 

(b) cos 327° 

(c) tan 248° 

(d) cos 213° 

3. Determine the following without the use of a calculator: 

(a) (tan 150°) (sin 30°) + cos 330° 

(b) (tan 300°) (cos 120°) 

(c) (1 - cos 30°)(1 - sin 210°) 

(d) cos 780° + (sin 315°) (tan 420°) 

4. Determine the following by reducing to an acute angle and using special angles. Do not use a 
calculator: 

(a) cos 300° 

(b) sin 135° 

(c) cos 150° 

(d) tan 330° 

(e) sin 120° 

(f) tan 2 225° 

(g) cos 315° 
(h) sin 2 420° 

(i) tan 405° 

(j) cos 1020° 

(k) tan 2 135° 

(I) 1 - sin 2 210° 



(/V 1 ) More practice Qt>J video solutions (9 J or help at www.everythingmaths.co.za 



(1.)014i (2.) 014j (3.) 014k (4.) 014m 

Function Values of (—6) 

When the argument of a trigonometric function is (— 9) we can add 360° without changing the result. 
Thus for sine and cosine 

sin(-6») = sin(360° - 9) = - sin 9 

cos(-6>) = cos(360° - 9) = cos9 
Function Values of 90° ± 6 



Activity: 



Reduction Formulae for Function Values of 90° ± 9 






1 . Function values of (90° — 9) 



172 



CHAPTER 17. TRIGONOMETRY 



17.3 



(a) In the figure P and P' lie on the cir- 
cle with radius 2. OP makes an angle 
9 = 30° with the x-axis. P thus has co- 
ordinates (\/3; 1). P' is the reflection of 
P about the line y = x. Using symmetry, 
write down the coordinates of P'. 

(b) Using the coordinates for P' determine 
sin(90° - 9), cos(90° - 9) and tan(90° - 



(c) From your results try and determine a re- 
lationship between the function values of 
(90° - 6) and 9. 

2. Function values of (90° + 9) 

(a) In the figure P and P' lie on the cir- 
cle with radius 2. OP makes an angle 
9 = 30° with the x-axis. P thus has co- 
ordinates (\/3;l). P' is the rotation of 
P through 90°. Using symmetry, write 
down the coordinates of P' . (Hint: con- 
sider P' as the reflection of P about the 
line y = x followed by a reflection about 
the y-axis) 

(b) Using the coordinates for P' determine 
sin(90° +9), cos(90° +9) and tan(90° + 
9). 

(c) From your results try and determine a re- 
lationship between the function values of 
(90° + 6) and 6. 





Complementary angles are positive acute angles that add up to 90°. For example 20° and 70° are 
complementary angles. 

Sine and cosine are known as co-functions. Two functions are called co-functions if f(A) = g{B) 
whenever A + B = 90° (i.e. A and B are complementary angles). The other trig co-functions are 
secant and cosecant, and tangent and cotangent. 

The function value of an angle is equal to the co-function of its complement (the co-co rule). 

Thus for sine and cosine we have 



sin(90° - 9) 
cos(90° - 9) 



cosy 
sinS 



Example 5: Co-function Rule 



QUESTION 



Write each of the following in terms of 40° using sin(90° 

1. cos 50° 

2. sin 320° 

3. cos 230° 



cos 9 and cos(90° — 9) = sin 9. 



173 



17.3 



CHAPTER 17. TRIGONOMETRY 



SOLUTION 



1. cos 50° = sin(90° - 50°) = sin 40° 

2. sin 320° = sin(360° - 40°) = -sin 40° 

3. cos 230° =cos(180° +50°) = -cos 50° 
= - sin(90° - 50° ) = - sin 40° 



Function Values of (9 - 90°) 

sin(6»-90°) = -cos6»andcos(6»-90°) = sin( 
These results may be proved as follows: 



sin(6»-90°) 



similarly, cos(9 — 90°) = sin (9 



sin[-(90° -6>)] 
-sin(90° -9) 
— cos 8 



Summary 

The following summary may be made 



Tip 



These reduction 
formulae hold 
for any angle 8. 
For convenience, 
we usually work 
with 6 as if it 
is acute, i.e. 
0° < 8 < 90°. 

When determin- 
ing function val- 
ues of 180° ± 
0, 360° ± and 
— the functions 
never change. 

When determin- 
ing function val- 
ues of 90° ± e 
and 6 - 90° the 
functions changes 
to its co-function 
(co-co rule). 



second quadrant (180° - 9) or (90° 


+ 8) 


first quadrant (9) or (90° - 9) 


sin(180° -9) = +sin0 






all trig functions are positive 


cos(180° -9) = -cos9 






sin(360° +9) = sm9 


tan(180° -9) = -tang 






cos(360° +9) = cos 9 


sin(90° + 9) = + cos 9 






tan(360° +9) = tan 9 


cos(90° +9) = -sine 






sin(90° - 9) = sin 9 
cos(90° -9) = cos9 


third quadrant (180° +9) 






fourth quadrant (360° — 9) 


sin(180° + 9) = -sin6» 






sin(360° -9) = -sin0 


cos(180° + 9) = -cos 6» 






cos(360° -9) = +cos9 


tan(180° +9) = +tan6» 






tan(360° - 9) = - tan 9 



Extension: 



Function Values of (270° ± 9) 



Angles in the third and fourth quadrants may be written as 270° ± 9 with 9 an acute angle. 
Similar rules to the above apply. We get 



third quadrant (270° 9) 

sin(270° - 6») = - cos 8 
cos(270° -6») = -sing 



fourth quadrant (270° + 9) 
sin(270° + 9) = -cos 9 
cos(270° +9) = +sin0 



174 



CHAPTER 17. TRIGONOMETRY 



17.4 




17.4 Solving Trigonometric 
Equations 




In Grade 10 and 1 1 we focused on the solution of algebraic equations and excluded equations that 
dealt with trigonometric functions (i.e. sin and cos). In this section, the solution of trigonometric 
equations will be discussed. 

The methods described in previous Grades also apply here. In most cases, trigonometric identities will 
be used to simplify equations, before finding the final solution. The final solution can be found either 
graphically or using inverse trigonometric functions. 



Graphical Solution 



EMBDF 



As an example, to introduce the methods of solving trigonometric equations, consider 

sinff = 0,5 (17.1) 

As explained in previous Grades,the solution of Equation 1 7.1 is obtained by examining the intersect- 
ing points of the graphs of: 

y = sin 8 

y = 0,5 

Both graphs, for —720° < 8 < 720°, are shown in Figure 1 7.9 and the intersection points of the graphs 
are shown by the dots. 




-720 - 



Figure 17.9: Plot of y = sin8 and y = 0,5 showing the points of intersection, hence the solutions to 
the equation sin 8 = 0,5. 

In the domain for 8 of —720° < 8 < 720°, there are eight possible solutions for the equation sin 9 = 
0,5. These are 8 = [-690°; -570°; -330°; -210°; 30°; 150°; 390°; 510°] 



175 



77.4 



CHAPTER 17. TRIGONOMETRY 



Example 6: 


QUESTION 


Find 8, iftand + 0,5 = 1,5, with 0° < 8 < 90°. Determine the solution graphically. 


SOLUTION 


Step 1 : Write the equation so that all the terms with the unknown quantity (i.e. 8) are 
on one side of the equation. 


tan<9 + 0,5 = 1,5 


tan 8 = 1 


Step 2 : Identify the two functions which are intersecting. 


y = tan 8 


y = i 


Step 3 : Draw graphs of both functions, over the required domain and identify the 
intersection point. 




J y = tan 8 




1 ii — 1 




J 

4 ' 1 > 


-1 - 


45 90 


The graphs intersect at 8 


1 

= 45°. 





Algebraic Solution 



EMBDG 



The inverse trigonometric functions can be used to solve trigonometric equations. These may be shown 
as second functions on your calculator: sin^ 1 , cos^ 1 and tanT 1 . 

Using inverse trigonometric functions, the equation 

sin0 = 0,5 



176 



CHAPTER 17. TRIGONOMETRY 



17.4 



is solved as 



On your calculator you would type 



This step does not need to be shown in your calculations. 





sin 


9 = 0,5 
= 30° 


sin 


( 


0,5 ) = 



to find the size of ( 



Example 7: 



QUESTION 



Find 9, if tan# + 0,5 = 1,5, with 0° < 9 < 90°. Determine the solution using inverse 
trigonometric functions. 



SOLUTION 



Step 1 : Write the equation so that all the terms with the unknown quantity (i.e. 9) are 
on one side of the equation. Then solve for the angle using the inverse function. 

tan<9 + 0,5 = 1,5 
tan 9 = 1 

= 45° 



Trigonometric equations often look very simple. Consider solving the equation sin# = 0,7. We can 
take the inverse sine of both sides to find that 9 = sin _1 (0,7). If we put this into a calculator we find 
that sin _1 (0,7) = 44,42°. This is true, however, it does not tell the whole story. 









i y 










1 - 








< / 1 — 

-360 


-188 


— ^-1 - 


f i 


18fX 


t| *■ 

y360 a 



Figure 1 7.10: The sine graph. The dotted line represents y = 0,7. There are four points of intersection 
on this interval, thus four solutions to sin 9 = 0,7. 

As you can see from Figure 1 7.1 0, there are four possible angles with a sine of 0,7 between —360° and 
360°. If we were to extend the range of the sine graph to infinity we would in fact see that there are an 



177 



17.4 CHAPTER 17. TRIGONOMETRY 



infinite number of solutions to this equation! This difficulty (which is caused by the periodicity of the 
sine function) makes solving trigonometric equations much harder than they may seem to be. 

Any problem on trigonometric equations will require two pieces of information to solve. The first is 
the equation itself and the second is the range in which your answers must lie. The hard part is making 
sure you find all of the possible answers within the range. Your calculator will always give you the 
smallest answer {i.e. the one that lies between —90° and 90° for tangent and sine and one between 0° 
and 180° for cosine). Bearing this in mind we can already solve trigonometric equations within these 
ranges. 



Example 8: 



QUESTION 



Find the values of x for which sin (§) = 0,5 if it is given that x < 90° 



SOLUTION 



Because we are told that x is an acute angle, we can simply apply an inverse trigonometric 
function to both sides. 



sin(f) 


= 


0,5 


=*§ 


= 


arcsin0,5 


=>f 


= 


30° 



(17.2) 
(17.3) 
(17.4) 
(17.5) 



We can, of course, solve trigonometric equations in any range by drawing the graph. 



Example 9: 



QUESTION 



For what values of x does sin a; = 0,5 when —360° < x < 360°? 



SOLUTION 



Step 1 : Draw the graph 

We take a look at the graph of sinx = 0,5 on the interval [—360°; 360°]. We 
want to know when the y value of the graph is 0,5 so we draw in a line at y = 0,5. 



178 



CHAPTER 17. TRIGONOMETRY 



17.4 




-360 



Step 2 : 



Notice that this line touches the graph four times. This means that there are four 
solutions to the equation. 



Step 3 : 



Read off the x values of those intercepts from the graph as x = —330°; —210°; 
30° and 150°. 




-360 



This method can be time consuming and inexact. We shall now look at how to solve these problems 
algebraically. 



Solution using CAST diagrams 



EMBDH 



The Sign of the Trigonometric Function 

The first step to finding the trigonometry of any angle is to determine the sign of the ratio for a given 
angle. We shall do this for the sine function first and then do the same for the cosine and tangent. 

In Figure 1 7.1 1 we have split the sine graph into four quadrants, each 90° wide. We call them quad- 
rants because they correspond to the four quadrants of the unit circle. We notice from Figure 17.1 1 that 
the sine graph is positive in the 1 st and 2 nd quadrants and negative in the 3 rd and 4 th . Figure 17.12 
shows similar graphs for cosine and tangent. 

All of this can be summed up in two ways. Table 1 7.7 shows which trigonometric functions are positive 
and which are negative in each quadrant. 

A more convenient way of writing this is to note that all functions are positive in the I s ' quadrant, 
only sine is positive in the 2 nd , only tangent in the 3 rd and only cosine in the 4 th . We express this 



179 



77.4 



CHAPTER 77. TRIGONOMETRY 




* 180' 



!)() 



/ 2 nd 


^X 


/ +VE 


+VE \ 


\ Ord 


4 th / 


\-VE 


-VE/ 



270 



0°/360° 



Figure 1 7.1 1 : The graph and unit circle showing the sign of the sine function. 



1 - 


I st 


rjnd 1 ord 1 AtYi ' 






r i$o° /to° 3$o° 


1 - 


+VE 


-VE | -VE | +V£ j 




-V.E 





-VE 




Figure 17.12: Graphs showing the sign of the cosine and tangent functions. 





-I st 


2 nd 


3 rd 


4 th 


sin 
cos 
tan 


+VE 
+VE 
+VE 


+VE 
-VE 
-VE 


-VE 
-VE 
+VE 


-VE 

+VE 
-VE 



Table 1 7.7: The signs of the three basic trigonometric functions in each quadrant. 



LSI) 



CHAPTER 17. TRIGONOMETRY 



17.4 



using the CAST diagram (Figure 17.13). This diagram is known as a CAST diagram as the letters, 
taken anticlockwise from the bottom right, read C-A-S-T. The letter in each quadrant tells us which 
trigonometric functions are positive in that quadrant. The A in the I s ' quadrant stands for all (meaning 
sine, cosine and tangent are all positive in this quadrant). S, C and T, of course, stand for sine, cosine 
and tangent. The diagram is shown in two forms. The version on the left shows the CAST diagram 
including the unit circle. This version is useful for equations which lie in large or negative ranges. The 
simpler version on the right is useful for ranges between 0° and 360°. Another useful diagram shown 
in Figure 1 7.1 3 gives the formulae to use in each quadrant when solving a trigonometric equation. 



mr 




0°/360° 



T 



180° - e 



c 



180° + 9 



360° - e 



270 : ' 



Figure 17.13: The two forms of the CAST diagram and the formulae in each quadrant. 



Magnitude of the Trigonometric Functions 

Now that we know in which quadrants our solutions lie, we need to know which angles in these 
quadrants satisfy our equation. 

Calculators give us the smallest possible answer (sometimes negative) which satisfies the equation. For 
example, if we wish to solve sin 6 = 0,3 we can apply the inverse sine function to both sides of the 
equation to find: 

sine = 0,3 
.-. 9 = 17,46° 

However, we know that this is just one of infinitely many possible answers. We get the rest of the 
answers by finding relationships between this small angle, 9, and answers in other quadrants. 
To do this we use our small angle 9 as a reference angle. We then look at the sign of the trigonometric 
function in order to decide in which quadrants we need to work (using the CAST diagram) and add 
multiples of the period to each, remembering that sine, cosine and tangent are periodic (repeating) 
functions. To add multiples of the period we use (360° . n) (where n is an integer) for sine and cosine 
and (180° . n); n e Z, for the tangent. 



Example 10: 



QUESTION 



Solve for 9: 



sine = 0,3 



SOLUTION 



181 



17.4 CHAPTER 17. TRIGONOMETRY 



Step 1 : Determine in which quadrants the solution lies 

We look at the sign of the trigonometric function. sin# is given 
as a positive amount (0,3). Reference to the CAST diagram shows 
that sine is positive in the first and second quadrants. 



T C 



Step 2 : Determine the reference angle 

The small angle 6 is the angle returned by the calculator: 

sin 6» = 0,3 
.'. 6 = 17,46° 

Step 3 : Determine the general solution 

Our solution lies in quadrants I and II. We therefore use 9 and iso° -e \ e 

180° - 9, and add the (360° . n) for the periodicity of sine. iso" +T\Tt 

1:6 = 17,46° + (360° . n); n e Z 
II : 6 = 180° - 17,46° + (360° . n); n 6 Z 
= 162,54° + (360° .7i); n 6 Z 

This is called the general solution. 

Step 4 : Find the specific solutions 

We can then find all the values of by substituting n = . . . — 1; 0: 1; 2; . . .etc. 

For example, 

|fn = 0, 6 = 17,46°; 162,54° 

|fn = l, 6 = 377,46°; 522,54° 

|fn = -l, 6» = -342,54°; -197,46° 

We can find as many as we like or find specific solutions in a given interval by 

choosing more values for n. 



General Solution Using Periodicity wembdi 



Up until now we have only solved trigonometric equations where the argument (the bit after the func- 
tion, e.g. the 6 in cos 6 or the (2x — 7) in tan(2x — 7)), has been 9. If there is anything more complicated 
than this we need to be a little more careful. 

Let us try to solve tan(2x — 10°) = 2,5 in the range —360° < x < 360°. We want solutions for 
positive tangent so using our CAST diagram we know to look in the I s ' and 3 rd quadrants. Our cal- 
culator tells us that 2x — 10° = 68,2°. This is our reference angle. So to find the general solution we 
proceed as follows: 



tan(2a; - 10 ) = 2,5 

.-. 2x-10° = 68,2° 

I: 2x-10° = 68,2° + (180°. n) 

2x = 78,2° + (180° .n) 

x = 39,1° + (90°.n); n e : 



lcS2 



CHAPTER 17. TRIGONOMETRY 17.4 

This is the general solution. Notice that we added the 10° and divided by 2 only at the end. Notice that 
we added (180° . n) because the tangent has a period of 180°. This is also divided by 2 in the last step 
to keep the equation balanced. We chose quadrants I and III because tan was positive and we used 
the formulae 9 in quadrant I and (180° +&) in quadrant 111. To find solutions where —360° < x < 360° 
we substitute integers for n: 

. n = 0;x = 39,1°; 219,1° 

. n = l; x = 129,1°; 309,1° 

. n = 2; x = 219,1°; 399,1° (too big!) 

. n = 3; x = 309,1°; 489,1° (too big!) 

• n = -l;x = -50,9°; 129,1° 

• n = -2; x = -140,9°; -39,9° 

• n = -3; x = -230,9°; -50,9° 
. n = -4; x = -320,9°; -140,9° 

• n = -5; x = -410,9°; -230,9° 

• n = -6; x = -500,9°; -320,9° 

Solution: x = -320,9°; -230°; -140,9°; -50,9°; 39,1°; 129,1°; 219,1° and 309,1° 




Just like with regular equations without trigonometric functions, solving trigonometric equations can 
become a lot more complicated. You should solve these just like normal equations to isolate a single 
trigonometric ratio. Then you follow the strategy outlined in the previous section. 



Example 11: 



QUESTION 



Write down the general solution for 3 cos(9 — 15°) — 1 = —2,583 



183 



17.4 CHAPTER 17. TRIGONOMETRY 



SOLUTION 


3cos(6>- 15°) - 1 




-2,583 


3cos(#- 15°) 


= 


-1,583 


cos(#- 15°) 


= 


-0,5276... 


reference angle: (6 — 15°) 


= 


58,2° 


II : 9 - 15° 


= 


180° - 58,2° + (360° . n); n e Z 


e 


= 


136,8° + (360°.n);n e Z 


III : 9 - 15° 


= 


180° + 58,2° + (360° . n); ra e Z 


e 




253,2° + (360° . n);n e Z 





Quadratic and Higher Order Trigonometric _ E/V(6D/C 
Equations 

The simplest quadratic trigonometric equation is of the form 

sin x — 2 = —1,5 

This type of equation can be easily solved by rearranging to get a more familiar linear equation 

sin x = 0,5 
=► sin x = ± v0>5 



This gives two linear trigonometric equations. The solutions to either of these equations will satisfy the 
original quadratic. 

The next level of complexity comes when we need to solve a trinomial which contains trigonometric 
functions. It is much easier in this case to use temporary variables. Consider solving 

tan 2 (2x + 1) + 3 tan (2x + 1) + 2 = 

Here we notice that tan(2z + 1) occurs twice in the equation, hence we let y = tan(2x + 1) and 
rewrite: 

y 2 + 3y + 2 = 

That should look rather more familiar. We can immediately write down the factorised form and the 
solutions: 

(y + l)(y + 2) = 
=>y = -l OR y = -2 



Next we just substitute back for the temporary variable: 

tan (2a; + 1) = -1 or tan(2x + l) = -2 



181 



CHAPTER 17. TRIGONOMETRY 17.4 



And then we are left with two linear trigonometric equations. Be careful: sometimes one of the two 
solutions will be outside the range of the trigonometric function. In that case you need to discard that 
solution. For example consider the same equation with cosines instead of tangents 

cos 2 (2x + 1) + 3 cos (2x + 1) + 2 = 

Using the same method we find that 

cos(2x + 1) = -1 or cos (2x + 1) = -2 

The second solution cannot be valid as cosine must lie between —1 and 1. We must, therefore, reject 
the second equation. Only solutions to the first equation will be valid. 



More Complex Trigonometric Equations wembdl 



Here are two examples on the level of the hardest trigonometric equations you are likely to encounter. 
They require using everything that you have learnt in this chapter. If you can solve these, you should 
be able to solve anything! 



Example 12: 



QUESTION 


Solve 2 cos 2 


x-cosx- 1 = Oforx e [-180°; 360°] 






SOLUTION 






Step 1 


Use a temporary variable 

We note that cos x occurs twice in the equation. So, let y = cos x 
2y 2 — y — 1 = Note that with practise you may be able to leave 


Then we have 
out this step. 


Step 2 


Solve the quadratic equation 

Factorising yields 

(2y + l)(y - 1) = 

V = -0,5 or y = 1 






Step 3 


Substitute back and solve the two resulting equations 

We thus get 

cos x = —0,5 or cosx = 1 

Both equations are valid (i.e. lie in the range of cosine). 
General solution: 







185 



17.4 CHAPTER 17. TRIGONOMETRY 



cosx = —0,5 [60°] 

II : x = 180° -60° + (360° ,n);neZ cosx = 1 [90°] 

= 120° + (360°.n);n e Z I; IV: x = 0°(360° . n);n 6 Z 

III: x = 180° + 60°(360°.n);ne Z = (360°.n);neZ 

= 240° + (360°.n);n G Z 

Now we find the specific solutions in the interval [—180°; 360°]. Appropri- 
ate values of n yield 



x = -120°;0 o ;120 o ;240 o ;360 o 



Example 13: 



QUESTION 



Solve for x in the interval [-360°; 360°].- 



SOLUTION 



Step 1 : Factorise 

Factorising yields 

sin x(2 sin x — cos x) = 

which gives two equations 

sin x = 



2 sin — cos x 


= 





2sinx 


= 


cosx 


2sinx 




cosx 


cosx 




cosx 


2 tanx 


= 


1 



tan x = j 

Step 2 : Solve the two trigonometric equations 

General solution: 

n rn °i tana; = \ [ 26 > 57 °1 

smx = z 

n „ n o v c „ I; HI: x = 26,57° + (180°. n);n e Z 

x = (180 . n);n 6 £ 

Specific solution in the interval [—360°; 360°]: 
x = -360°; -206,57°; -180°; -26,57°; 0°; 26,57°; 180°; 206,25°; 360° 



Lsfi 



CHAPTER 17. TRIGONOMETRY 



17.4 



Exercise 17-10 



1 . (a) Find the general solution of each of the following equations. Give answers to one decimal 
place. 

(b) Find all solutions in the interval 9 £ [-180°; 360°]. 

sin 6» = -0,327 
cos (9 = 0,231 
tan0= -1,375 
iv. sin<9 = 2,439 



Find the general solution of each of the following equations. Give answers to one decimal 
place. 



2. (a) 

(b) Find all solutions in the interval 9 e [0°;360 



cos 9 = 
sin6»= & 
i. 2 cos 6» - y/E = 
iv. tan 9 = — 1 
v. 5cos# = —2 
vi. 3sin6» = -1,5 
vii. 2 cos 6» + 1,3 = 
viii. 0,5 tan + 2,5= 1,7 



3. (a) 

(b) 

4. (a) 

(b) 

5. (a) 

(b) 

6. (a) 

(b) 

7. (a) 

(b) 



Write down the general solution for a; if tana; ; 
Hence determine values of x e [—180°; 180°]. 

Write down the general solution for 9 if sm9 = 
Hence determine values of 9 e [0°; 720°]. 

Solve for A if sin{A + 20°) = 0,53 
Write down the values of A e [0°; 360°] 

Solve for x if cos(x + 30°) = 0,32 

Write down the values of x e [-180°; 360°] 

Solve for 9 if sin 2 {9) + 0,5 sin 9 = 
Write down the values of 9 e [0°; 360°] 



-1,12. 



-0,61. 



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(l.)014n (2.)014p (3.) 014q (4.) 014r (5.) 014s (6.) 014t 
(7.) 014u 



187 



77.5 



CHAPTER 17. TRIGONOMETRY 




17.5 Sine and Cosine Identities 




There are a few identities relating to the trigonometric functions that make working with triangles 
easier. These are: 

1. the sine rule 

2. the cosine rule 

3. the area rule 

and will be described and applied in this section. 



The Sine Rule 



EMBDN 



DEFINITION: 


The Sine Rule 












The sine rule appl 


es to any triangle: 
sin A 

Q 


sinB 

b 


sinC 
c 








where a is the side 


opposite A, b is the 


side opposite B and 


c is 


the side 


opposite C. 



Consider AABC. 




The area of AABC can be written as: 



area AABC = -c.h. 

2 



However, h can be calculated in terms of A or B as: 



sin A 



and 



h = b . sin A 

sin B = — 

a 

h = a . sinB 



INS 



CHAPTER 17. TRIGONOMETRY 



17.5 



Therefore the area of AABC is: 



c. h 

c.b . sin A 

c.a . sin B 



Similarly, by drawing the perpendicular between point B and line AC we can show that: 

—c.b . sin A = —a . b . sinC 
2 2 



Therefore the area of AABC is: 



—c.b . sin A = -c.a . s'mB = —a . b . sinC 



If we divide through by \a . b . c, we get: 



sin A sin B sin C 



This is known as the sine rule and applies to any triangle, right-angled or not. 



Example 14: Lighthouses 



QUESTION 




255° 



There is a coastline with two lighthouses, one on either side of a beach. The two lighthouses 
are 0,67 km apart and one is exactly due east of the other. The lighthouses tell how close a 
boat is by taking bearings to the boat (remember - a bearing is an angle measured clockwise 
from north). These bearings are shown. Use the sine rule to calculate how far the boat is from 
each lighthouse. 



18!) 



77.5 



CHAPTER 17. TRIGONOMETRY 




255° 



SOLUTION 

We can see that the two lighthouses and the boat form a triangle. Since we know the dis- 
tance between the lighthouses and we have two angles we can use trigonometry to find the 
remaining two sides of the triangle, the distance of the boat from the two lighthouses. 



0.67 km 




We need to know the lengths of the two sides AC and BC. We can use the sine rule to 
find our missing lengths. 



BC 

sin A 

BC 



AB 
sin C 
AB . sin A 

sinC 
(0,67)sin(37°) 

sin(128°) 
0,51 km 



AC 
s'mB 

AC 



AB 
sin (7 
AB . sin B 

s'mC 
(0,67)sin(15°) 

sin(128°) 
0,22 km 



190 



CHAPTER 17. TRIGONOMETRY 



17.5 



Exercise 17-11 



1 . Show that 



is equivalent to: 



i A sin B sin 



a b c 

sin A sin B sin C 



Note: either of these two forms can be used. 

2. Find all the unknown sides and angles of the following triangles: 

(a) APQR in which Q = 64°; R = 24° and r = 3 

(b) AKLM in which K = 43°; M = 50° and m = 1 

(c) AABC in which A = 32,7°; C = 70,5° and a = 52,3 

(d) AXYZ in which X = 56°; Z = 40° and x = 50 

3. In AABC, i = 116°; C = 32° and AC = 23 m. Find the length of the side AB. 

4. In ARST, R = 19°; S = 30° and RT = 120 km. Find the length of the side 8T. 

5. In ARMS, K = 20°; M = 100° and s = 23 cm. Find the length of the side m. 



I\n More practice (►) video solutions f'fj or help at www.everythingmaths.co.za 



(1.)014v (2.) 014w (3.)014x (4.) 014y (5.) 014z 



The Cosine Rule 



EMBDO 



DEFINITION: The Cosine Rule 












The cosine rule applies to any triangle and states that: 










2 

a 


= b + c - 


- 26c cos A 










b 2 


2 . 2 

= c + a - 


- 2ca cos B 










2 
C 


2 i >2 

= a + b - 


- 2afecosC 










where a is the side opposite A, 


b is the side opposite B and c 


is the s 


de 


oppos 


ted. 



The cosine rule relates the length of a side of a triangle to the angle opposite it and the lengths of the 
other two sides. 

Consider AABC which we will use to show that: 



191 



77.5 



CHAPTER 17. TRIGONOMETRY 




a = (c — d) + h 



In ADCB: 

from the theorem of Pythagoras. 
In AACD: 



from the theorem of Pythagoras. 

We can eliminate h 2 from (1 7.6) and (1 7.7) to get: 

b — d = a — (c — d) 



a 2 = b 2 + {c 2 -2cd + d 2 )-d 2 



In order to eliminate d we look at AACD, where we have: 

A d 

cos A = —. 



(17.6) 



(17.7) 



(17.8) 



So, 



Substituting this into (1 7.8), we get: 



d = b cos A. 



a = b + c — 26c cos A 



(17.9) 



The other cases can be proved in an identical manner. 



Example 15: 



QUESTION 



Find A: 




192 



CHAPTER 17. TRIGONOMETRY 



17.5 



SOLUTION 


Applying the cosine rule: 










2 

a 


= 


b + c — 26c cos A 




cos A 


= 


6 2 + c 2 - a 1 


26c 








8 2 + 5 2 - 7 2 








2.8.5 






= 


0,5 




.-. A 




60° 





Exercise 17-12 



1 . Solve the following triangles i.e. find all unknown sides and angles 

(a) AABC in which A = 70°; 6 = 4 and c = 9 

(b) AXYZ in which Y = 112°; x = 2 and y = 3 

(c) AJJST in which RS = 2; ST = 3 and KT = 5 

(d) AKLM in which A'L = 5; LAI = 10 and KM = 7 

(e) AJH K in which if = 130°; JH = 13 and HK = 8 

(f) ADEF in which ci = 4; e = 5 and / = 7 

2. Find the length of the third side of the AXYZ where: 

(a) X = 71,4°; y = 3,42 km and z = 4,03 km 

(b) ; x = 103,2 cm; Y = 20,8° and z = 44,59 cm 

3. Determine the largest angle in: 

(a) AJHK in which JH = 6; HK = 4 and JK = 3 

(b) APQR where p = 50; <j = 70 and r = 60 



Aj More practice f ►) video solutions (9) or help at www.everythingmaths.co.za 



(1.) 0150 (2.) 0151 (3.) 0152 



193 



77.5 



CHAPTER 17. TRIGONOMETRY 



The Area Rule 



EMBDP 



DEFINITION: The Area Rule 

The area rule applies to any triangle and states that the area of a triangle is given by 
half the product of any two sides with the sine of the angle between them. 



That means that in the ADEF, the area is given by: 

1 



-DE.EFsinE 



-EF .FD sin F 

2 

-FD. DE sin D 




In order show that this is true for all triangles, consider AABC. 




The area of any triangle is half the product of the base and the perpendicular height. For AABC, this 
is: 



However, h can be written in terms of A as: 



A = -c.h. 
2 



h = 6 sin A 



So, the area of AABC is: 



A = — c. 6 sin A. 



Using an identical method, the area rule can be shown for the other two angles. 



191 



CHAPTER 17. TRIGONOMETRY 



17.5 



Example 16: The Area Rule 



QUESTION 



Find the area of AABC: 




SOLUTION 



AABC is isosceles, therefore AB = AC = 7 and C = B = 50°. Hence A = 180° - 50° 
50° = 80°. Now we can use the area rule to find the area: 



1 
2 
1 
2 
24,13 



cb sin A 

. 7 . 7 . sin 80° 



Exercise 17-13 



Draw sketches of the figures you use in this exercise. 

1 . Find the area of APQR in which: 

(a) P = 40°; q = 9 and r = 25 

(b) Q = 30°; r = 10 and p = 7 

(c) R= 110°; p= Sand (j = 9 

2. Find the area of: 

(a) AXYZ with XY = 6 cm; XZ = 7 cm and Z = 28° 

(b) APQR with PR = 52 cm; PQ = 29 cm and P = 58,9° 

(c) AEFG with FG = 2,5 cm; EG = 7,9 cm and G = 125° 

3. Determine the area of a parallelogram in which two adjacent sides are 10 cm and 13 cm and the 
angle between them is 55°. 

4. If the area of AABC is 5000 m 2 with a = 150 m and 6 = 70 m, what are the two possible sizes 
ofC? 



195 



77.5 



CHAPTER 17. TRIGONOMETRY 



CjX*j More practice (►) video solutions (9) or help at www.everythingmaths 



(1.) 01 53 (2.) 0154 (3.) 0155 (4.) 0156 




Summary of the Trigonometric 
Rules and Identities 




Squares Identity Quotient Identity 
cos 2 9 + sin 2 8 = 1 tan 

Odd/Even Identities Periodicity Identities 



sin(— 8) = — sin 6 
cos(— 8) = cos 8 

Sine Rule 



in A sin B 



sin(6»±360°) = sin 6 
cos(8 ± 360° ) = cos ( 

Area Rule 

Area = | be cos A 
Area = \ac cos B 
Area = i a 5 C osC 



sin 9 
cos 6 



Cofunction Identities 



sin(90° -8) = cos 6» 
cos(90° -6>) = sin0 

Cosine Rule 

2 = b 2 + c 2 -2bccosA 
2 = a 2 + c 2 — 2accosB 
2 = a 2 + b 2 -2abcosC 



Chapter 1 7 



End of Chapter Exercises 



Q is a ship at a point 10 km due South of another ship P. R is a 

lighthouse on the coast such that P = Q = 50°. 

Determine: 

(a) the distance QR 

(b) the shortest distance from the lighthouse to the line joining the 
two ships (PQ). 




10 km 



19(5 



CHAPTER 17. TRIGONOMETRY 



17.5 



1 . WXYZ is a trapezium (WX || XZ) with WI = 3 m; 
YZ = 1,5 m;Z = 120° and VF = 30°. 

Determine the distances XZ and XY, 



1,5 m 




3 m 



2. On a flight from Johannesburg to Cape Town, the pilot discovers that he has been 
flying 3° off course. At this point the plane is 500 km from Johannesburg. The direct 
distance between Cape Town and Johannesburg airports is 1 552 km. Determine, to 
the nearest km: 

(a) The distance the plane has to travel to get to Cape Town and hence the extra 
distance that the plane has had to travel due to the pilot's error. 

(b) The correction, to one hundredth of a degree, to the plane's heading (or direc- 
tion). 

3. ABCD is a trapezium (i.e. AB || CD). AB = x; 
BAD = a; BCD = b and BDC = c. 
Find an expression for the length of CD in terms of 
x, a, b and c. 



A surveyor is trying to determine the distance between 
points X and Z. However the distance cannot be de- 
termined directly as a ridge lies between the two points. 
From a point Y which is equidistant from X and Z, he 
measures the angle XYZ. 




(a) If XY = x and XYZ = 9, show that XZ 
x-j2(\ -cos0). 

(b) Calculate XZ (to the nearest kilometre) if x 
240 km and 6 = 132°. 



5. Find the area of WXYZ (to two decimal places): 




6. Find the area of the shaded triangle in terms of x, a, f3, 
8 and <j>; 




E D 



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eo solutions 



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(1.) 0157 (2.) 0158 (3.) 0159 (4.) 015a (5.) 015b (6.) 015c 
(7.) 015d 



197 



Statistics 





18.1 Introduction 




This chapter gives you an opportunity to build on what you have learned in previous grades about 
data handling and probability. The work done will be mostly of a practical nature. Through problem 
solving and activities, you will end up mastering further methods of collecting, organising, displaying 
and analysing data. You will also learn how to interpret data, and not always to accept the data at 
face value, because data is sometimes misused and abused in order to try to falsely prove or support a 
viewpoint. Measures of central tendency (mean, median and mode) and dispersion (range, percentiles, 
quartiles, inter-quartile, semi-inter-quartile range, variance and standard deviation) will be investigated. 
Of course, the activities involving probability will be familiar to most of you - for example, you may 
have played dice or card games even before you came to school. Your basic understanding of proba- 
bility and chance gained so far will deepen to enable you to come to a better understanding of how 
chance and uncertainty can be measured and understood. 

© See introductory video: VMfvd at www.everythingmaths.co.za 




18.2 Standard Deviation and 
Variance 




The measures of central tendency (mean, median and mode) and measures of dispersion (quartiles, 
percentiles, ranges) provide information on the data values at the centre of the data set and provide 
information on the spread of the data. The information on the spread of the data is however based on 
data values at specific points in the data set, e.g. the end points for range and data points that divide 
the data set into four equal groups for the quartiles. The behaviour of the entire data set is therefore 
not examined. 

A method of determining the spread of data is by calculating a measure of the possible distances 
between the data and the mean. The two important measures that are used are called the variance and 
the standard deviation of the data set. 



Variance 



EMBDT 



The variance of a data set is the average squared distance between the mean of the data set and each 
data value. An example of what this means is shown in Figure 18.1. The graph represents the results 
of 1 00 tosses of a fair coin, which resulted in 45 heads and 55 tails. The mean of the results is 50. The 
squared distance between the heads value and the mean is (45 — 50) 2 = 25 and the squared distance 
between the tails value and the mean is (55 — 50) 2 = 25. The average of these two squared distances 
gives the variance, which is |(25 + 25) = 25. 



198 



CHAPTER 18. STATISTICS 



18.2 



60 -r 

55 

50 

45 

40 

35 

30 

25 

20 

15 

10 

5 





Tails-Mean 
Heads-Mean 



Heads Tails 

Face of Coin 



Figure 18.1 : The graph shows the results of 100 tosses of a fair coin, with 45 heads and 55 tails. The 
mean value of the tosses is shown as a vertical dotted line. The difference between the mean value 
and each data value is shown. 

Population Variance 

Let the population consist of n elements {xi; xi\ . . . ;x n }, with mean x (read as "x bar"). The variance 
of the population, denoted by a 2 , is the average of the square of the distance of each data value from 
the mean value. 



(E(*-^)) 2 



(18.1) 



Since the population variance is squared, it is not directly comparable with the mean and the data 
themselves. 

Sample Variance 

Let the sample consist of the n elements {xi,x 2 , . . . ,i„}, taken from the population, with mean x. The 
variance of the sample, denoted by s 2 , is the average of the squared deviations from the sample mean: 



n- 1 



(18.2) 



Since the sample variance is squared, it is also not directly comparable with the mean and the data 
themselves. 

A common question at this point is "Why is the numerator squared?" One answer is: to get rid of the 
negative signs. Numbers are going to fall above and below the mean and, since the variance is looking 
for distance, it would be counterproductive if those distances factored each other out. 

Difference between Population Variance and Sample Variance 

As seen a distinction is made between the variance, a 2 , of a whole population and the variance, s 2 of 
a sample extracted from the population. 

When dealing with the complete population the (population) variance is a constant, a parameter which 
helps to describe the population. When dealing with a sample from the population the (sample) 
variance varies from sample to sample. Its value is only of interest as an estimate for the population 
variance. 



19!) 



18.2 CHAPTER 18. STATISTICS 



Properties of Variance 

The variance is never negative because the squares are always positive or zero. The unit of variance 
is the square of the unit of observation. For example, the variance of a set of heights measured in 
centimetres will be given in square centimeters. This fact is inconvenient and has motivated many 
statisticians to instead use the square root of the variance, known as the standard deviation, as a 
summary of dispersion. 



Standard Deviation wembdu 



Since the variance is a squared quantity, it cannot be directly compared to the data values or the mean 
value of a data set. It is therefore more useful to have a quantity which is the square root of the variance. 
This quantity is known as the standard deviation. 

In statistics, the standard deviation is the most common measure of statistical dispersion. Standard 
deviation measures how spread out the values in a data set are. More precisely, it is a measure of the 
average distance between the values of the data in the set and the mean. If the data values are all 
similar, then the standard deviation will be low (closer to zero). If the data values are highly variable, 
then the standard variation is high (further from zero). 

The standard deviation is always a positive number and is always measured in the same units as the 
original data. For example, if the data are distance measurements in metres, the standard deviation 
will also be measured in metres. 



Population Standard Deviation 

Let the population consist of n elements {xi;x 2 ; . ..;#„}, with mean x. The standard deviation of the 
population, denoted by a, is the square root of the average of the square of the distance of each data 
value from the mean value. 

^ (X ~ X)2 (18.3) 



Sample Standard Deviation 

Let the sample consist of n elements {xi;x 2 ;...,x n }, taken from the population, with mean x. The 
standard deviation of the sample, denoted by s, is the square root of the average of the squared 
deviations from the sample mean: 



E(X ~" )2 (18.4) 

n — 1 

It is often useful to set your data out in a table so that you can apply the formulae easily. For example to 
calculate the standard deviation of {57; 53; 58; 65; 48; 50; 66; 51}, you could set it out in the following 
way: 

sum of items 



number of items 



448 

~8~ 
56 



201) 



CHAPTER 18. STATISTICS 



18.2 



Note: To get the deviations, subtract each number from the mean. 



X 


Deviation (X 


-X) 


Deviation squared (X - 


-xf 


57 




1 




1 




53 




-3 




9 




58 




2 




4 




65 




9 




81 




48 




-8 




64 




50 




-6 




36 




66 




10 




100 




51 




-5 




25 




£* = 


= 448 


v> = o 


J2(X~ x f = 320 



Note: The sum of the deviations of scores about their mean is zero. This always happens; that is 
(X — X) = 0, for any set of data. Why is this? Find out. 

Calculate the variance (add the squared results together and divide this total by the number of items). 



Variance = 


n 
320 


= 


8 
10 




ard deviation 


•/variance 




= 


U:(x-xr 

V n 






/320 






V 8 




= 


Vio 




= 


6.32 



Difference between Population Variance and Sample Variance 

As with variance, there is a distinction between the standard deviation, a, of a whole population and 
the standard deviation, s, of sample extracted from the population. 

When dealing with the complete population the (population) standard deviation is a constant, a pa- 
rameter which helps to describe the population. When dealing with a sample from the population the 
(sample) standard deviation varies from sample to sample. 

In other words, the standard deviation can be calculated as follows: 

1. Calculate the mean value x. 

2. For each data value x, calculate the difference xt — x between x t and the mean value x. 

3. Calculate the squares of these differences. 

4. Find the average of the squared differences. This quantity is the variance, a' 1 . 

5. Take the square root of the variance to obtain the standard deviation, a. 

© See video: VMfvk at www.everythingmaths.co.za 



201 



18.2 



CHAPTER 18. STATISTICS 



Example 1: Variance and Standard Deviation 



QUESTION 



What is the variance and standard deviation of the population of possibilities associated with 
rolling a fair die? 



SOLUTION 



Step I : Determine how many outcomes make up the population 

When rolling a fair die, the population consists of 6 possible outcomes. The data 
set is therefore x = {1; 2; 3; 4; 5; 6}. and n = 6. 



Step 2 : Calculate the population mean 

The population mean is calculated by: 



x = -(1 + 2 + 3 + 4 + 5 + 6) 
= 3,5 



Step 3 : Calculate the population variance 

The population variance is calculated by: 

J2(x-x) 2 



- (6,25 + 2,25 + 0,25 + 0,25 + 2,25 + 6,25) 
2,917 



Step 4 : Alternately the population variance is calculated by: 



X 


(X-X) 


(X-X) 2 


1 


-2.5 


6.25 




2 


-1.5 


2.25 




3 


-0.5 


0.25 




4 


0.5 


0.25 




5 


1.5 


2.25 




6 


2.5 


6.25 




£X = 21 


E* = o 


E(x-x) 2 = 


= 17.5 



Step 5 : Calculate the standard deviation 

The (population) standard deviation is calculated by: 



= 1,708. 

Notice how this standard deviation is somewhere in between the possible devia- 
tions. 



202 



CHAPTER 18. STATISTICS 18.2 



Interpretation and Application Pfmbdv 



A large standard deviation indicates that the data values are far from the mean and a small standard 
deviation indicates that they are clustered closely around the mean. 

For example, each of the three samples (0; 0; 14; 14), (0; 6; 8; 14), and (6; 6; 8; 8) has a mean of 7. Their 
standard deviations are 8,08; 5,77 and 1,15 respectively. The third set has a much smaller standard 
deviation than the other two because its values are all close to 7. The value of the standard deviation 
can be considered large' or 'small' only in relation to the sample that is being measured. In this case, 
a standard deviation of 7 may be considered large. Given a different sample, a standard deviation of 7 
might be considered small. 

Standard deviation may be thought of as a measure of uncertainty. In physical science for example, 
the reported standard deviation of a group of repeated measurements should give the precision of 
those measurements. When deciding whether measurements agree with a theoretical prediction, the 
standard deviation of those measurements is of crucial importance: if the mean of the measurements is 
too far away from the prediction (with the distance measured in standard deviations), then we consider 
the measurements as contradicting the prediction. This makes sense since they fall outside the range 
of values that could reasonably be expected to occur if the prediction were correct and the standard 
deviation appropriately quantified. (See prediction interval.) 



Relationship Between Standard Deviation ^embdw 
and the Mean 



The mean and the standard deviation of a set of data are usually reported together. In a certain 
sense, the standard deviation is a "natural" measure of statistical dispersion if the centre of the data is 
measured about the mean. 



Exercise 18-1 



1 . Bridget surveyed the price of petrol at petrol stations in Cape Town and Durban. The raw data, 
in rands per litre, are given below: 



Cape Town 


3,96 


3,76 


4,00 


3,91 


3,69 


3,72 


Durban 


3,97 


3,81 


3,52 


4,08 


3,88 


3.68 



(a) Find the mean price in each city and then state which city has the lowest mean. 

(b) Assuming that the data is a population find the standard deviation of each city's prices. 

(c) Assuming the data is a sample find the standard deviation of each city's prices. 

(d) Giving reasons which city has the more consistently priced petrol? 

2. The following data represents the pocket money of a sample of teenagers. 
150; 300; 250; 270; 130; 80; 700; 500; 200; 220; 110; 320; 420; 140. 
What is the standard deviation? 

3. Consider a set of data that gives the weights of 50 cats at a cat show. 

(a) When is the data seen as a population? 

(b) When is the data seen as a sample? 



20:! 



18.3 



CHAPTER 18. STATISTICS 



4. Consider a set of data that gives the results of 20 pupils in a class. 

(a) When is the data seen as a population? 

(b) When is the data seen as a sample? 



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1 8.3 Graphical Representation of Measures 
of Central Tendency and Dispersion 




The measures of central tendency (mean, median, mode) and the measures of dispersion (range, semi- 
inter-quartile range, quartiles, percentiles, inter-quartile range) are numerical methods of summarising 
data. This section presents methods of representing the summarised data using graphs. 



Five Number Summary 



EMBDY 



One method of summarising a data set is to present a five number summary. The five numbers are: 
minimum, first quartile, median, third quartile and maximum. 



Box and Whisker Diagrams 



EMBDZ 



A box and whisker diagram is a method of depicting the five number summary, graphically. 

The main features of the box and whisker diagram are shown in Figure 18.2. The box can lie horizon- 
tally (as shown) or vertically. For a horizontal diagram, the left edge of the box is placed at the first 
quartile and the right edge of the box is placed at the third quartile. The height of the box is arbitrary, 
as there is no y-ax\s. Inside the box there is some representation of central tendency, with the median 
shown with a vertical line dividing the box into two. Additionally, a star or asterix is placed at the 
mean value, centred in the box in the vertical direction. The whiskers which extend to the sides reach 
the minimum and maximum values. 



201 



CHAPTER 18. STATISTICS 



18.3 



first 
quartile \ 


median 


third 
/ quartile 


i 


i 


minimum 


maximum 


data value 




data value 


-4 


2 2 4 
Data Values 



Figure 18.2: Main features of a box and whisker diagram 



Example 2: Box and Whisker Diagram 



QUESTION 



Draw a box and whisker diagram for the data set 

x = {1,25; 1,5; 2,5; 2,5; 3,1; 3,2; 4,1; 4,25; 4,75; 4,8; 4,95; 5,1}. 



SOLUTION 



Step 1 : Determine the five number summary 

Minimum = 1,25 
Maximum = 5,10 

Position of first quartile = between 3 and 4 
Position of second quartile = between 6 and 7 
Position of third quartile = between 9 and 10 

Data value between 3 and 4 = 1(2,5 + 2,5) = 2,5 
Data value between 6 and 7 = 1(3,2 + 4,1) = 3,65 
Data value between 9 and 10 = 1(4,75 + 4,8) = 4,775 

The five number summary is therefore: 1,25; 2,5; 3,65; 4,775; 5,10. 

Step 2 : Draw a box and whisker diagram and mark the positions of the minimum, 
maximum and quartiles. 



first third 

quartile quartile 

median 



minimum 



maximum 



12 3 4 

Data Values 



205 



18.3 CHAPTER 18. STATISTICS 



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Exercise 18-2 



1. Lisa works as a telesales person. She keeps a record of the number of sales she makes each 
month. The data below show how much she sells each month. 

49; 12; 22; 35; 2; 45; 60; 48; 19; 1; 43; 12 

Give a five number summary and a box and whisker plot of her sales. 

2. Jason is working in a computer store. He sells the following number of computers each month: 
27; 39; 3; 15; 43; 27; 19; 54; 65; 23; 45; 16 

Give a five number summary and a box and whisker plot of his sales, 

3. The number of rugby matches attended by 36 season ticket holders is as follows: 
15; 11; 7; 34; 24; 22; 31; 12; 9 

12; 9; 1; 3; 15; 5; 8; 11; 2 
25; 2; 6; 18; 16; 17; 20; 13; 17 
14; 13; 11; 5; 3; 2; 23; 26; 40 



(a) Sum the data. 

(b) Using an appropriate graphical method (give reasons) represent the data. 

(c) Find the median, mode and mean. 

(d) Calculate the five number summary and make a box and whisker plot. 

(e) What is the variance and standard deviation? 

(f) Comment on the data's spread. 

(g) Where are 95% of the results expected to lie? 

4. Rose has worked in a florists shop for nine months. She sold the following number of wedding 
bouquets: 

16; 14; 8; 12; 6; 5; 3; 5; 7 

(a) What is the five-number summary of the data? 

(b) Since there is an odd number of data points what do you observe when calculating the 
five-numbers? 



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Cumulative Histograms wembea 



Cumulative histograms, also known as ogives, are a plot of cumulative frequency and are used to 
determine how many data values lie above or below a particular value in a data set. The cumulative 
frequency is calculated from a frequency table, by adding each frequency to the total of the frequencies 
of all data values before it in the data set. The last value for the cumulative frequency will always be 



206 



CHAPTER 18. STATISTICS 



18.3 



equal to the total number of data values, since all frequencies will already have been added to the 
previous total. The cumulative frequency is plotted at the upper limit of the interval. 

For example, the cumulative frequencies for Data Set 2 are shown in Table 18.2 and is drawn in 
Figure 18.3. 



Intervals 


< n< 1 


1 < n < 2 


2 < n < 3 


3 < n < 4 


4 < n < 5 


5 < n < 6 


Frequency 


30 


32 


35 


34 


37 


32 


Cumulative 
Frequency 


30 


30 + 32 


30+32+35 


30 + 32 + 
35 + 34 


30 + 32 + 
35+34+37 


30 + 32 + 
35 + 34 + 
37 + 32 




30 


62 


97 


131 


168 


200 



Table 18.1: Cumulative Frequencies for Data Set 2. 




Figure 18.3: Example of a cumulative histogram for Data Set 2. 

Notice the frequencies plotted at the upper limit of the intervals, so the points (30; 1) (62; 2) (97; 3), 
etc have been plotted. This is different from the frequency polygon where we plot frequencies at the 
midpoints of the intervals. 



Exercise 18-3 



1 . Use the following data of peoples ages to answer the questions. 
2; 5; 1; 76; 34; 23; 65; 22; 63; 45; 53; 38 

4; 28; 5; 73; 80; 17; 15; 5; 34; 37; 45; 56 

(a) Using an interval width of 8 construct a cumulative frequency distribution 

(b) How many are below 30? 

(c) How many are below 60? 

(d) Giving an explanation state below what value the bottom 50% of the ages fall 

(e) Below what value do the bottom 40% fall? 

(f) Construct a frequency polygon and an ogive. 

(g) Compare these two plots 

2. The weights of bags of sand in grams is given below (rounded to the nearest tenth): 
50.1; 40.4; 48.5; 29.4; 50.2; 55.3; 58.1; 35.3; 54.2; 43.5 

60.1; 43.9; 45.3; 49.2; 36.6; 31.5; 63.1; 49.3; 43.4; 54.1 



207 



18.4 



CHAPTER 18. STATISTICS 



(a) Decide on an interval width and state what you observe about your choice. 

(b) Give your lowest interval. 

(c) Give your highest interval. 

(d) Construct a cumulative frequency graph and a frequency polygon. 

(e) Compare the cumulative frequency graph and frequency polygon. 

(f) Below what value do 53% of the cases fall? 

(g) Below what value of 60% of the cases fall? 



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18.4 Distribution of Data 




Symmetric and Skewed Data 



EMBEC 



The shape of a data set is important to know. 



DEFINITION: Shape of a data set 
This describes how the data is distributed relative to the mean and median. 



Symmetrical data sets are balanced on either side of the median. 



Skewed data is spread out on one side more than on the other. It can be skewed right or skewed 
left. 



skewed right 



skewed left 



20N 



CHAPTER 18. STATISTICS 



18.4 



Relationship of the Mean, Median, and 
Mode 



EMBED 



The relationship of the mean, median, and mode to each other can provide some information about 
the relative shape of the data distribution. If the mean, median, and mode are approximately equal 
to each other, the distribution can be assumed to be approximately symmetrical. With both the mean 
and median known, the following can be concluded: 

• (mean - median) ra then the data is symmetrical 

• (mean - median) > then the data is positively skewed (skewed to the right). This means that 
the median is close to the start of the data set. 

• (mean - median) < then the data is negatively skewed (skewed to the left). This means that the 
median is close to the end of the data set. 



Exercise 18-4 



1 . Three sets of 12 pupils each had test score recorded. The test was out of 50. Use the given data 
to answer the following questions. 



Set A 


SetB 


SetC 


25 


32 


43 


47 


34 


47 


15 


35 


16 


17 


32 


43 


16 


25 


38 


26 


16 


44 


c24 


38 


42 


27 


47 


50 


22 


43 


50 


24 


29 


44 


12 


18 


43 


31 


25 


42 



Table 18.2: Cumulative Frequencies for Data Set 2. 



(a) For each of the sets calculate the mean and the five number summary. 

(b) For each of the classes find the difference between the mean and the median. Make box 
and whisker plots on the same set of axes. 

(c) State which of the three are skewed (either right or left). 

(d) Is set A skewed or symmetrical? 

(e) Is set C symmetrical? Why or why not? 

Two data sets have the same range and interquartile range, but one is skewed right and the other 
is skewed left. Sketch the box and whisker plots and then invent data (6 points in each set) that 
meets the requirements. 



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20!) 



78.5 



CHAPTER 18. STATISTICS 




18.5 Scatter Plots 




A scatter-plot is a graph that shows the relationship between two variables. We say this is bivariate data 
and we plot the data from two different sets using ordered pairs. For example, we could have mass on 
the horizontal axis (first variable) and height on the second axis (second variable), or we could have 
current on the horizontal axis and voltage on the vertical axis. 

Ohm's Law is an important relationship in physics. Ohm's law describes the relationship between 
current and voltage in a conductor, like a piece of wire. When we measure the voltage (dependent 
variable) that results from a certain current (independent variable) in a wire, we get the data points as 
shown in Table 18.3. 



Table 18.3: Values of current and voltage measured in a wire. 



Current 


Voltage 


Current 


Voltage 





0.4 


2.4 


1.4 


0.2 


0.3 


2.6 


1.6 


0.4 


0.6 


2.8 


1.9 


0.6 


0.6 


3 


1.9 


0.8 


0.4 


3.2 


2 


1 


1 


3.4 


1.9 


1.2 


0.9 


3.6 


2.1 


1.4 


0.7 


3.8 


2.1 


1.6 


1 


4 


2.4 


1.8 


1.1 


4.2 


2.4 


2 


1.3 


4.4 


2.5 


2.2 


1.1 


4.6 


2.5 



When we plot this data as points, we get the scatter plot shown in Figure 1 8.4. 



2 -- 



1 -- 






12 3 4 

Current 



Figure 18.4: Example of a scatter plot 



If we are to come up with a function that best describes the data, we would have to say that a straight 
line best describes this data. 



210 



CHAPTER 18. STATISTICS 



18.5 



Extension: 



Ohm's Law 



Ohm's Law describes the relationship between current and voltage in a conductor. The gradi- 
ent of the graph of voltage vs. current is known as the resistance of the conductor. 



Activity: 



Scatter Plot 



The function that best describes a set of data can take any form. We will restrict ourselves 
to the forms already studied, that is, linear, quadratic or exponential. Plot the following sets of 
data as scatter plots and deduce the type of function that best describes the data. The type of 
function can either be quadratic or exponential. 



3. 





X 


y 


X 


y 


X 


y 


X 


y 




-5 


9.8 





14.2 


-2.5 


11.9 


2.5 


49.3 


1 


-4.5 


4.4 


0.5 


22.5 


-2 


6.9 


3 


68.9 




-4 


7.6 


1 


21.5 


-1.5 


8.2 


3.5 


88.4 




-3.5 


7.9 


1.5 


27.5 


-1 


7.8 


4 


117.2 




-3 


7.5 


2 


41.9 


-0.5 


14.4 


4.5 


151.4 


















X 


y 


X 


y 


X 


y 


X 


y 




-5 


75 





5 


-2.5 


27.5 


2.5 


7.5 


? 


-4.5 


63.5 


0.5 


3.5 


-2 


21 


3 


11 




-4 


53 


1 


3 


-1.5 


15.5 


3.5 


15.5 




-3.5 


43.5 


1.5 


3.5 


-1 


11 


4 


21 




-3 


35 


2 


5 


-0.5 


7.5 


4.5 


27.5 



Height (cm) 


117 
168 


150 
170 


152 
173 


155 
175 


157 
178 


160 
180 


163 
183 


165 


Weight (kg) 


52 
63 


53 
64 


54 
66 


56 
68 


57 
70 


59 
72 


60 

74 


61 



DEFINITION: outlier 

A point on a scatter plot which is widely separated from the other points or a result 
differing greatly from others in the same sample is called an outlier. 



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Exercise 18-5 



1 . A class's results for a test were recorded along with the amount of time spent studying for it. The 
results are given below. 



211 



78.5 



CHAPTER 18. STATISTICS 



Score (percent) 


Time spent studying 


(minutes) 


67 


100 




55 


85 




70 


150 




90 


180 




45 


70 




75 


160 




50 


80 




60 


90 




84 


110 




30 


60 




66 


96 




96 


200 





(a) Draw a diagram labelling horizontal and vertical axes. 

(b) State with reasons, the cause or independent variable and the effect or dependent variable. 

(c) Plot the data pairs 

(d) What do you observe about the plot? 

(e) Is there any pattern emerging? 

2. The rankings of eight tennis players is given along with the time they spend practising. 



Practise time (min) 


Ranking 


154 


5 


390 


1 


130 


6 


70 


8 


240 


3 


280 


2 


175 


4 


103 


7 



(a) Construct a scatter plot and explain how you chose the dependent (cause) and independent 
(effect) variables. 

(b) What pattern or trend do you observe? 

3. Eight children's sweet consumption and sleep habits were recorded. The data is given in the 
following table. 



Number of sweets (per week) 


Average sleeping time (per day) 


15 


4 


12 


4.5 


5 


8 


3 


8.5 


18 


3 


23 


2 


11 


5 


4 


8 



(a) What is the dependent (cause) variable? 

(b) What is the independent (effect) variable? 

(c) Construct a scatter plot of the data. 

(d) What trend do you observe? 



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212 



CHAPTER 18. STATISTICS 



18.6 




18.6 Misuse of Statistics 




Statistics can be manipulated in many ways that can be misleading. Graphs need to be carefully anal- 
ysed and questions must always be asked about "the story behind the figures." Potential manipulations 
are: 



1 . Changing the scale to change the appearance of a graph 

2. Omissions and biased selection of data 

3. Focus on particular research questions 

4. Selection of groups 



Activity: 



Misuse of statistics 



1 . Examine the following graphs and comment on the effects of changing scale. 





213 



78.6 



CHAPTER 18. STATISTICS 



2. Examine the following three plots and comment on omission, selection and bias. Hint: 
What is wrong with the data and what is missing from the bar and pie charts? 



Activity 


Hours 


Sleep 


8 


Sports 


2 


School 


7 


Visit friend 


1 


Watch TV 


2 


Studying 


3 



if) 



9 -- 



5 -- 



2 -- 





211 



CHAPTER 18. STATISTICS 



18.6 



Exercise 18-6 



The bar graph below shows the results of a study that looked at the cost of food compared to the 
income of a household in 1994. 



12 



o 

a 10 



S. 4 



n 




o 



Income in 1 994 (in thousands of rands) 



Income (thousands of rands) 


Food bill (thousands of rands) 


<5 


2 


5-10 


2 


10-15 


4 


15-20 


4 


20-30 


8 


30-40 


6 


40-50 


10 


> 50 


12 



1 . What is the dependent variable? Why? 



2. What conclusion can you make about this variable? Why? Does this make sense? 



3. What would happen if the graph was changed from food bill in thousands of rands to percentage 
of income? 



4. Construct this bar graph using a table. What conclusions can be drawn? 



5. Why do the two graphs differ despite showing the same information? 



6. What else is observed? Does this affect the fairness of the results? 



215 



78.6 



CHAPTER 18. STATISTICS 



(/V 1 ) More practice (►) video solutions Ccj or help at www.everythingmaths.c 



(1.) 01 5v 



Chapter 1 8 



End of Chapter Exercises 



1. Many accidents occur during the holidays between Durban and Johannesburg. A 
study was done to see if speeding was a factor in the high accident rate. Use the 
results given to answer the following questions. 



Speed (km/h) 


Frequency 


60 < x < 70 


3 


70 < x < 80 


2 


80 < x < 90 


6 


90 < x < 100 


40 


100 < x < 110 


50 


110 < x < 120 


30 


120 < x < 130 


15 


130 < x < 140 


12 


140 < x < 150 


3 


150 < x < 160 


2 



(a) Draw a graph to illustrate this information. 

(b) Use your graph to find the median speed and the interquartile range. 

(c) What percent of cars travel more than 120 km/h on this road? 

(d) Do cars generally exceed the speed limit? 

The following two diagrams (showing two schools contribution to charity) have been 
exaggerated. Explain how they are misleading and redraw them so that they are not 
misleading. 



/ 


/ 


R100 




R100 


R100 


/ 




R200.00 



3. The monthly income of eight teachers are given as follows: 

R10 050; R14 300; R9 800; R15 000; R12 140; R13 800; Rll 990; R12 900. 



216 



CHAPTER 18. STATISTICS 18.6 



(a) What is the mean income and the standard deviation? 

(b) How many of the salaries are within one standard deviation of the mean? 

(c) If each teacher gets a bonus of R500 added to their pay what is the new mean 
and standard deviation? 

(d) If each teacher gets a bonus of 10% on their salary what is the new mean and 
standard deviation? 

(e) Determine for both of the above, how many salaries are within one standard 
deviation of the mean. 

(f) Using the above information work out which bonus is more beneficial financially 
for the teachers. 



f/Vj More practice CrJ video solutions Cf) or help at www.everythingmaths.co.za 



(1.) 0161 (2.) 0162 (3.) 0163 



217 



Independent and Dependent 
Events 




19.1 Introduction 




In probability theory events are either independent or dependent. This chapter discusses the differ- 
ences between these two categories of events and will show that we use different sets of mathematical 
rules for handling them. 

© See introductory video: VMgdw at www.everythingmaths.co.za 




19.2 Definitions 




Two events are independent if knowing something about the value of one event does not give any 
information about the value of the second event. For example, the event of getting a "1" when a die is 
rolled and the event of getting a "1" the second time it is thrown are independent. 

The probability of two independent events occurring, P(A n B), is given by: 

P{AnB) = P(A) x P(B) (19.1) 



DEFINITION: Independent events 

Events are said to be independent if the result or outcome of one event does not 
affect the result or outcome of the other event. So P(A/C) = P{A), where P(A/C) 
represents the probability of event A after event C has occurred. 



Example 1: Independent Events 



QUESTION 



What is the probability of rolling a 1 and then rolling a 6 on a fair die? 



SOLUTION 



218 



CHAPTER 19. INDEPENDENT AND DEPENDENT EVENTS 19.2 



Step 1 : Identify the two events and determine whether the events are independent or 
not 

Event A is rolling a 1 and event B is rolling a 6. Since the outcome of the 
first event does not affect the outcome of the second event, the events are inde- 
pendent. 



Step 2 : Determine the probability of the specific outcomes occurring, for each event 

The probability of rolling a 1 is | and the probability of rolling a 6 is |. 
Therefore, P(A) = § and P(B) = \. 



Step 3 : Use equation 19.1 to determine the probability of the two events occurring 
together. 



P(AnB) = P(A)xP(B) 
1 1 
= 6 X 6 
1 
36 



The probability of rolling a 1 and then rolling a 6 on a fair die is ^ 



Consequently, two events are dependent if the outcome of the first event affects the outcome of the 
second event. 



DEFINITION: Dependent events 

Two events are dependent if the outcome of one event is affected by the outcome of 
the other event i.e. P(A/C) ^ P(A). 



Example 2: Dependent Events 



QUESTION 



A cloth bag has four coins, one Rl coin, two R2 coins and one R5 coin. What is the probability 
of first selecting a Rl coin and then selecting a R2 coin? 



SOLUTION 



21!) 



79.2 CHAPTER 19. INDEPENDENT AND DEPENDENT EVENTS 



Step 1 : Identify the two events and determine whether the events are independent or 
not 

Event A is selecting a Rl coin and event B is next selecting a R2. Since the 
outcome of the first event affects the outcome of the second event (because there 
are less coins to choose from after the first coin has been selected), the events are 
dependent. 



Step 2 : Determine the probability of the specific outcomes occurring, for each event 

The probability of first selecting a Rl coin is \ and the probability of next 
selecting a R2 coin is | (because after the Rl coin has been selected, there are 
only three coins to choose from). 

Therefore, P(A) = \ and P(B) = §. 



Step 3 : Use equation 19.1 to determine the probability of the two events occurring 
together. 

The same equation as for independent events are used, but the probabilities 
are calculated differently. 

P(AnB) = P(A) x P(B) 
1 2 
= 4 X 3 
2 

12 
1 



The probability of first selecting a Rl coin followed by selecting a R2 coin is 



Identification of Independent and Depen- 
dent Events 

Use of a Contingency Table 

A two-way contingency table (studied in an earlier grade) can be used to determine whether events are 
independent or dependent. 



EMBEI 



DEFINITION: two-way contingency table 

A two-way contingency table is used to represent possible outcomes when two events 
are combined in a statistical analysis. 



220 



CHAPTER 19. INDEPENDENT AND DEPENDENT EVENTS 



19.2 



For example we can draw and analyse a two-way contingency table to solve the following problem. 



Example 3: Contingency Tables 



QUESTION 



A medical trial into the effectiveness of a new medication was carried out. 120 males and 
90 females responded. Out of these 50 males and 40 females responded positively to the 
medication. 



1 . Was the medication's success independent of gender? Explain. 

2. Give a table for the independence of gender results. 



SOLUTION 



Step 1 : Draw a contingency table 





Male 


Female 


Totals 


Positive result 
No Positive result 


50 
70 


40 
50 


90 
120 


Totals 


120 


90 


210 



Step 2 : Work out probabilities 



120 
P(maIe).P(positive result) = — — = 0,57 

90 
P(femaIe).P(positive result) = — — = 0,43 

50 
P(male and positive result) = — — = 0,24 



Step 3 : Draw conclusion 

P(male and positive result) is the observed probability and P(maIe).P(positive 
result) is the expected probability. These two are quite different. So there is no 
evidence that the medication's success is independent of gender. 

Step 4 : Gender-independent results 

To get gender independence we need the positive results in the same ratio as the 
gender. The gender ratio is: 120 : 90, or 4 : 3, so the number in the male and 
positive column would have to be f of the total number of patients responding 
positively which gives 51,4. This leads to the following table: 





Male 


Female 


Totals 


Positive result 
No Positive result 


51,4 
68,6 


38,6 
51,4 


90 
120 


Totals 


120 


90 


210 



221 



19.2 



CHAPTER 19. INDEPENDENT AND DEPENDENT EVENTS 



Use of a Venn Diagram 

We can also use Venn diagrams to check whether events are dependent or independent. 

Also note that P(A/C) = F p^2-f ' ■ For example, we can draw a Venn diagram and a contingency 
table to illustrate and analyse the following example. 



Example 4: Venn diagrams and events 



QUESTION 



A school decided that its uniform needed upgrading. The colours on offer were beige or 
blue or beige and blue. 40% of the school wanted beige, 55% wanted blue and 15%sa/d a 
combination would be fine. Are the two events independent? 



SOLUTION 



Step 1 : Draw a Venn diagram 



s 


Beige 




Blue 






0,25 


0,15 


0,4 


0,2 



Step 2 : Draw up a contingency table 





Beige 


Not Beige 


Totals 


Blue 
Not Blue 


0,15 
0,25 


0,4 
0,2 


0,55 
0,35 


Totals 


0,40 


0,6 


1 



Step 3 : Work out the probabilities 

P(Blue)= 0,4; P(Beige)= 0,55; P(Both)= 0,15; P(Neither)= 0,20 
Probability of choosing beige after blue is: 



222 



CHAPTER 19. INDEPENDENT AND DEPENDENT EVENTS 19.2 



/ Beige ^ P(Beigen Blue) 



V Blue J P(BIue) 

0,15 
(^55 
= 0,27 



Step 4 : Solve the problem 

Since P ( R . - J the events are statistically dependent. 



Extension: 



Applications of Probability Theory 



Two major applications of probability theory in everyday life are in risk assessment and in trade 
on commodity markets. Governments typically apply probability methods in environmental 
regulation where it is called "pathway analysis", and are often measuring well-being using 
methods that are stochastic in nature, and choosing projects to undertake based on statistical 
analyses of their probable effect on the population as a whole. It is not correct to say that 
statistics are involved in the modelling itself, as typically the assessments of risk are one-time 
and thus require more fundamental probability models, e.g. "the probability of another 9/1 1 ". 
A law of small numbers tends to apply to all such choices and perception of the effect of such 
choices, which makes probability measures a political matter. 

A good example is the effect of the perceived probability of any widespread Middle East 
conflict on oil prices - which have ripple effects in the economy as a whole. An assessment by 
a commodity trade that a war is more likely vs. less likely sends prices up or down, and signals 
other traders of that opinion. Accordingly, the probabilities are not assessed independently nor 
necessarily very rationally. The theory of behavioural finance emerged to describe the effect 
of such groupthink on pricing, on policy, and on peace and conflict. 

It can reasonably be said that the discovery of rigorous methods to assess and combine 
probability assessments has had a profound effect on modern society. A good example is the 
application of game theory, itself based strictly on probability, to the Cold War and the mutual 
assured destruction doctrine. Accordingly, it may be of some importance to most citizens 
to understand how odds and probability assessments are made, and how they contribute to 
reputations and to decisions, especially in a democracy. 

Another significant application of probability theory in everyday life is reliability. Many 
consumer products, such as automobiles and consumer electronics, utilise reliability theory in 
the design of the product in order to reduce the probability of failure. The probability of failure 
is also closely associated with the product's warranty. 



Chapter 19 



End of Chapter Exercises 



1 . In each of the following contingency tables give the expected numbers for the events 
to be perfectly independent and decide if the events are independent or dependent. 



22:! 



19.2 



CHAPTER 19. INDEPENDENT AND DEPENDENT EVENTS 



(a) 





Brown eyes 


Not Brown eyes 


Totals 


Black hair 
Red hair 


50 
70 


30 

80 


80 
150 


Totals 


120 


110 


230 





(b) 




Point A 


Point B 


Totals 






Busses left late 
Buses left on time 


15 
25 


40 
20 


55 
45 






Totals 


40 


60 


100 




















Durban 


Bloemfontein 


Totals 


(c) 


Liked living there 
Did not like living there 


130 
140 


30 
200 


160 
340 




Totals 


270 


230 


500 





Multivitamin A 


Multivitamin B 


Totals 


Improvement in health 
No improvement in health 


400 
140 


300 
120 


700 
260 


Totals 


540 


420 


960 



(d) 



2. A study was undertaken to see how many people in Port Elizabeth owned either a 
Volkswagen or a Toyota. 3% owned both, 25% owned a Toyota and 60% owned a 
Volkswagen. Draw a contingency table to show all events and decide if car owner- 
ship is independent. 

3. Jane invested in the stock market. The probability that she will not lose all her money 
is 0,32. What is the probability that she will lose all her money? Explain. 

4. If D and F are mutually exclusive events, with P(D') = 0,3 and P(D or F) = 0,94, 
find P(F). 

5. A car sales person has pink, lime-green and purple models of car A and purple, 
orange and multicolour models of car B. One dark night a thief steals a car. 

(a) What is the experiment and sample space? 

(b) Draw a Venn diagram to show this. 

(c) What is the probability of stealing either a model of A or a model off?? 

(d) What is the probability of stealing both a model of A and a model of f?? 

6. The probability of Event X is 0,43 and the probability of Event Y is 0,24. The prob- 
ability of both occurring together is 0,10. What is the probability that X or Y will 
occur (this includes X and Y occurring simultaneously)? 

7. P(H) = 0,62; P(J) = 0,39 andP(ff and J) = 0,31. Calculate: 

(a) P(H') 

(b) P(H or J) 

(c) P(H' or J') 

(d) P(H' or J) 

(e) P(H' and J') 

8. The last ten letters of the alphabet were placed in a hat and people were asked to 
pick one of them. Event D is picking a vowel, Event E is picking a consonant and 
Event F is picking the last four letters. Calculate the following probabilities: 

(a) P(F') 

(b) P(F ox D) 

(c) P(neither E nor F) 

(d) P(D and E) 

(e) P(E and F) 

(f) P(E and D') 

9. At Dawnview High there are 400 Grade 12's. 270 do Computer Science, 300 do 
English and 50 do Typing. All those doing Computer Science do English, 20 take 
Computer Science and Typing and 35 take English and Typing. Using a Venn diagram 
calculate the probability that a pupil drawn at random will take: 

(a) English, but not Typing or Computer Science 



221 



CHAPTER 19. INDEPENDENT AND DEPENDENT EVENTS 19.2 



(b) English but not Typing 

(c) English and Typing but not Computer Science 

(d) English or Typing 



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(1.) 0164 (2.) 0165 (3.) 0166 (4.) 0167 (5.) 0168 (6.) 0169 
(7.) 016a (8.) 016b (9.) 016c 



22.") 



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