Quit

Introduction Complex Numbers The Argand Diagram Modulus

Quit Mathematicians have a concept called completeness. It is the need to be able to answer every single question. Historically it is this need for completeness which led the Hindus to discover negative numbers. Later the Greeks developed the idea of irrational numbers. Introduction

Quit During the sixteenth century, an Italian called Rafaello Bombelli came up with the question: “If the square root of +1 is both +1 and –1, then what is the square root of –1?” He answered the question himself and declared that In your own life you develop through all these stages of number. Rafaello Bombelli – 1 = i, an imaginary number.

Quit N: Natural numbers – these are whole positive numbers. These are the first numbers people understand, e.g. you are three years old and fighting with your little sister because she has three sweets and you have only two! Z: Integers – positive and negative whole numbers. Later in life, perhaps when you are five years old you understand the idea of minus numbers. You may have five sweets but you owe your friend two sweets, so you realise that in fact, you really only have three sweets, 5 – 2 = 3. Rafaello Bombelli

Quit R: Real Numbers – all numbers on the number line. Later again in life you realise that there are fractions and decimals. You may divide a bar of chocolate with eight squares and give your brother three squares and keep five for yourself. Other real numbers include: Rafaello Bombelli 3838 __ 5858 He gets of the bar and you get of it. THIS IS PROBABLY WHERE YOU ARE NOW! THIS IS PROBABLY WHERE YOU ARE NOW! 4, 2·114, – 3·49, 3, 9  –

Quit Complex Numbers These are numbers with a real and an imaginary part. They are written as a + ib where a and b are real numbers. –1 = i i 2 = –1

Quit Simply add the real parts, then add the imaginary parts i 6 + 2i + –––––– 9 + 7i Addition

Quit – ‘Change the sign on the lower line and add’ 8 – 3i 3 2i – –––––– 11 – 5i Subtraction + – + +

Quit Each part of the first complex number must be multiplied by each part of the second complex number. Multiplication i 2 = –1

Quit 4(3 + 2i)= 12 i2 = –1i2 = –1 = 12i + 8 = 12i – 8 = – i + 8i+ 8i = 12i + 8i 2 (–1) 4i(3 + 2i) Multiplication

Quit (3 + 2i)(4 + 5i) = 12 i2 = –1i2 = –1 = i + 8i + 10 = i + 8i – 10 = 2= i+ 8i + 10i 2 (–1) + 23i Collect real and imaginary parts Multiplication

Quit To divide complex numbers we need the concept of the complex conjugate. The conjugate of a complex number is the same number with the sign of the imaginary part changed. The conjugate of 5 + 3i is 5 – 3i. Division

Quit To divide we multiply the top and bottom by the conjugate of the bottom. Division

Quit 15 Division 9 – 8i i– 12i – 16i 2 = i 2 = –1 i 2 = – i 3 + 4i 3 – 4i × – 20i+ 6i+ 6i (–1) –––––––––––––––––– 15 – 20i + 6i = –––––––––––––– 23 – 14i 25 = –––––––

Quit A farmer has 100 m of fence to surround a small vegetable plot. The farmer wants to enclose a rectangular area of 400 m 2. How long and wide should it be? Application y x 50 – x 2 lengths + 2 widths = 100 2x + 2y = 100 x + y = 50

Quit The area = Length  width 400 = x(50 – x) 400 = 50x – x 2 x 2 – 50x = 0 x 50 – x

Quit b  4ac 2 2a2a x = b b  = 40 or 10 x 2 – 50x = 0 a = 1 b = – 50 c = 400 ––––––––––––––– (–50) 2 – 4(1)(400) 2(1) x = –  (–50)  –––––––––––––––––––––––– ––––––––––––––––– 2500 – = 50  ––––––––––– 2 = 50   30 –––––––

Quit A farmer has 100 m of fence to surround a small vegetable plot. The farmer wants to enclose a rectangular area of 650 m 2. How long and wide should it be? Application y x 50 – x 2 lengths + 2 widths = 100 2x + 2y = 100 x + y = 50

Quit The area = Length  width 650 = x(50 – x) 650 = 50x – x 2 x 2 – 50x = 0 x 50 – x

Quit b  4ac 2 2a2a x = b b  x 2 – 50x = 0 a = 1 b = – 50 c = 650 ––––––––––––––– (–50) 2 – 4(1)(650) 2(1) x = –  (–50)  –––––––––––––––––––––––– ––––––––––––––––– 2500 – = 50  ––––––––––––––––– –––––––––––– – = 50  ––– = –– ––––––––––––––   –1 –––––––– 2 50  10i = i 2 = –1 = 25  5i

Quit The German mathematician Carl Fredrich Gauss (1777 – 1855) proposed the Argand diagram. This has the real numbers on the x-axis and the imaginary ones on the y-axis. All complex numbers can be plotted and are usually called z 1, z 2 etc. The Argand Diagram

Quit Re Im 4 -4 The Argand Diagram z1z1 z2z2 z4z4 z3z3 z5z5 z 1 = (2 + 4i) z 2 = (–2 – 4i) z 3 = (4 + 0i) z 4 = (–3 + 0i) z 5 = (–3 + 2i)

Quit | 2 + 4i | = = = 20  z  = x 2 + y 2 z 1 = 2 + 4i | 4 + 0i | = = 16 z 3 = 4 + 0i = 4 Modulus

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