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1. Real Numbers and Complex Numbers. Case Study. 1.1 Real Number System. 1.2 Surds. 1.3 Complex Number System. Chapter Summary. I think I can do it by drawing a square of side 1 first.

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real numbers and complex numbers

1

Real Numbers and Complex Numbers

Case Study

1.1 Real Number System

1.2 Surds

1.3 Complex Number System

Chapter Summary

slide2

I think I can do it by drawing a square

of side 1 first.

If you are given a pair of compasses and a ruler only, do you know how to represent the irrational number

on a number line?

In junior forms, we learnt from Pythagoras’ theorem that the diagonal of a square of side 1 is .

The point of intersection of the arc and the number line is the position of (i.e., point C).

Case Study

As shown in the figure, after drawing the diagonal of the square, we can use a pair of compasses to draw an arc with radius OB and O as the centre.

1 1 real number system
1.1 Real Number System

.

1, 2, 4, 7, 0, , 2.5, 0.16, p, , …

.

0.16 means 0.166 666…

We often encounter different numbers in our calculations,

For example,

These numbers can be classified into different groups.

1 1 real number system1
1.1 Real Number System

Zero is neither positive nor negative.

Integers

7, 4, 0, 1, 2

Negative Integers

Positive Integers

(Natural Numbers)

A. Integers

1, 2, 4, 7 and 0 are all integers.

Positive integers (natural numbers) are integers that are greater than zero.

Negative integers are integers that are less than zero.

slide5

is a fraction, 2.5 is a terminating decimal and

0.16 is a recurring decimal.

.

Recurring decimals are also called repeating decimals.

Recurring decimals can be converted into fractions, as shown in the next page.

A rational number is a number that can be written in

the form , where p and q are integers and q 0.

and .

Any integer n can be written as . Therefore, integers are also

rational numbers.

1.1 Real Number System

B. Rational Numbers

All of them are rational numbers.

Note that

slide6

.

Express 0.16 as a fraction:

.

Let n  0.16

n 

. .

..

In other recurring decimals, such as a 0.83 and b 0.803,

. .

..

consider 100a 83.83 and 1000b 803.803, then we obtain

99a 83 and 999b 803.

1.1 Real Number System

B. Rational Numbers

 0.166 666… ............ (1)

10n  1.666 66… ............ (2)

(2)  (1): 10n n  1.5

9n  1.5

slide7

Numbers that cannot be written in the form are irrational

numbers.

Examples: p, , and sin 45

is just an approximation

of p.

1.1 Real Number System

C. Irrational Numbers

Irrational numbers can only be written as non-terminating and non-recurring decimals:

slide8

Real numbers

.

1, 2, 4, 7, 0, , 3.5, 0.16, p,

Rational numbers

Irrational numbers

.

p,

1, 2, 4, 7, 0, , 3.5, 0.16

Fractions

Terminating

decimals

Recurring

decimals

Integers

Negative integers

Zero

Positive integers

1.1 Real Number System

D. Real Numbers

If we group all the rational numbers and irrational numbers together, we have the real number system.

That is, a real number is either a rational number or an irrational number.

slide9

p

1

2.5

.

.

.

.

.

.

 is a real number since .

 is not a real number since .

1.1 Real Number System

D. Real Numbers

We can represent any real number on a straight line called the real number line.

Real numbers have the following property:

a2 0 for all real numbers a.

For example:

1 2 surds
1.2 Surds

1.

2.

In general,

In junior forms, we learnt the following properties for surds:

For any real numbers a and b, we have

1 2 surds1
1.2 Surds

A. Simplification of Surds

For any surds, when we reduce the integer inside the square root sign to the smallest possible integer, such as:

then the surd is said to be in its simplest form.

1 2 surds2
1.2 Surds

Like surds are surds with the same integer inside the square root sign, such as and .

B. Operations of Surds

When two surds are like surds, we can add them or subtract them:

slide13

Simplify .

1.2 Surds

B. Operations of Surds

Example 1.1T

Solution:

slide14

Simplify .

1.2 Surds

B. Operations of Surds

Example 1.2T

Solution:

slide15

Simplify .

1.2 Surds

B. Operations of Surds

Example 1.3T

Solution:

1 2 surds3
1.2 Surds

C. Rationalization of the Denominator

Rationalization of the denominator is the process of changing an irrational number in the denominator into a rational number, such as:

slide17

Simplify .

1.2 Surds

C. Rationalization of the Denominator

Example 1.4T

Solution:

1 3 complex number system
1.3 Complex Number System

Define .

Then

 is a real number since .

Complex numbers

 is not a real number since .

A. Introduction to Complex Numbers

In Section 1.1, we learnt that

a2 0 for all real numbers a.

For example:

Therefore, in a real number system, equations such as x21 and (x 1)24 have no real solution:

i

12i

slide19

1.3 Complex Number System

A. Introduction to Complex Numbers

Properties of complex numbers:

1. The complex number system contains an imaginary unit, denoted by i, such that

i21.

2. The standard form of a complex number is

abi,

where a and b are real numbers.

3. All real numbers belong to the complex number system.

slide20

Complex numbers do not have order. So we cannot compare which of the complex numbers 2  3i and 4  2i is greater.

1.3 Complex Number System

A. Introduction to Complex Numbers

Notes:

1. For a complex number abi, a is called the real part and b is called the imaginary part.

2. When a 0, abi0bibi, which is a purely imaginary number.

3. When b 0, abia 0ia, so any real number can be considered as a complex number.

4. When a b 0, abi 0  0i 0.

Two complex numbers are said to be equal if and only if both of their real parts and imaginary parts are equal.

If a, b, c and d are real numbers, then

abicdi

if and only if a  c and b  d.

slide21

In the operation of algebraic expressions, only like terms can be added or subtracted.

1.3 Complex Number System

B. Operations of Complex Numbers

The addition, subtraction, multiplication and division of complex numbers are similar to the operations of algebraic expressions.

We classify the real part and the imaginary part of the complex number as unlike terms in algebraic expressions.

For complex numbers z1  abi and z2  cdi, where a, b, c and d are real numbers, we have:

(1) Addition

z1 z2 (abi)  (cdi)

e.g. (3 6i)  (5  8i)

 abi cdi

 (3 5)  [6  (8)]i

 (ac)  (b d)i

 8  2i

slide22

1.3 Complex Number System

B. Operations of Complex Numbers

(2) Subtraction

z1  z2 (abi)  (cdi)

e.g. (9 7i)  (2  3i)

 abi cdi

 (9 2)  [7  (3)]i

 (ac)  (b d)i

 7  4i

(3) Multiplication

This term belongs to the real part because i2 1.

z1z2 (abi)(cdi)

 acadi bcibdi2

 (acbd)  (ad bc)i

slide23

 33  19i

1.3 Complex Number System

B. Operations of Complex Numbers

Example 1.5T

Simplify (7  2i)(5  3i)  4i(3  i).

Solution:

(7  2i)(5  3i)  4i(3  i)  (35  21i 10i 6i2)  (12i  4i2)

 35  21i 10i 6 12i  4

slide24

The denominator contains .

(p  q)(p  q)  p2 q2

The process of division is similar to the rationalization of the denominator in surd.

1.3 Complex Number System

B. Operations of Complex Numbers

(4) Division

slide25

Simplify and express the answer in standard form.

1.3 Complex Number System

B. Operations of Complex Numbers

Example 1.6T

Solution:

slide26

Real numbers

Rational numbers

Irrational numbers

Fractions

Terminating

decimals

Recurring

decimals

Integers

Negative integers

Zero

Positive integers

Chapter Summary

1.1 Real Number System

1 2 surds4

(a)

(b)

Chapter Summary

1.2 Surds

1. For any positive real numbers a and b:

2. For any positive real numbers a and b:

1 3 complex number system1

Chapter Summary

1.3 Complex Number System

1. Every complex number can be written in the form abi, where a and b are real numbers.

2. The operations of complex numbers obey the same rules as those of real numbers.