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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,608

Complex Number Formulas

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 20,902

Complex Numbers

A complex number is a number of the form a+bi and it consists of the real part and the imaginary part.

In a+bi, a is the real part and bi is the imaginary part.

i is an imaginary number, i=√(-1)

In polar form the complex number is represented as

r(Cosθ +iSinθ)

rCosθ =a and rSinθ =b; tanθ =b/a.

r is the modulus and θ is the argument.

In exponential form, a complex number is represented as

De Moivre's theorem:-

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**ganesh****Moderator**- Registered: 2005-06-28
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If

For every complex number z, there exists and inverse such that

Division of two complex numbers:-

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**ganesh****Moderator**- Registered: 2005-06-28
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The conjugate of a complex number z=a+bi is given by

Some of the properties of conjugates are

=

=

Re(z) is the Real part of x and Im(z) is the imaginary part of z.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 20,902

**Cube roots of unity**

Let z denote a cube root of unity.

or

Properties of cube roots of unity:-

(1) Each of the complex roots of cube root of unity is square of the other.

(2) Sum of the cube roots of unity is zero. i.e.

where 1, are the cube roots of unity.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**ganesh****Moderator**- Registered: 2005-06-28
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**Applications of De Moivre's Theorem in finding Roots of Complex Numbers**

Let z = x +iy

In polar form,

where

and

where k=0,1,2,3,...(n-1).

This gives n distinct roots of z.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**ganesh****Moderator**- Registered: 2005-06-28
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**nth roots of unity**

Let x be a root of unity. Then

where r=0,1,2,....n-1 using De Moivre's Theorem.

Let

The nth roots of unity are where r=0,1,2,3,4...(n-1).

That is, the nth roots of unity are

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**ganesh****Moderator**- Registered: 2005-06-28
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**Properties of arguments**

(1) The argument of a positive real number is zero.

(2) The argument of a negative real number is

.(3) The argument of a positive imaginary number is

.(4) The argument of a negative imaginary number is

or .Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**ganesh****Moderator**- Registered: 2005-06-28
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**Division and Exponentiation**

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**ganesh****Moderator**- Registered: 2005-06-28
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**de Moivre's identity for powers of Complex Numbers of Real n**

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**ganesh****Moderator**- Registered: 2005-06-28
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**Powers of Comples Numbers**

A power of complex number z to a positive integer exponent n can be written in closed form as

The first few are explicitly

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**Identity****Member**- Registered: 2007-04-18
- Posts: 934

**Properties of the magnitude:**

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**Ritu****Member**- Registered: 2011-08-09
- Posts: 1

(-1)^(1/3) is????

*Last edited by Ritu (2011-08-09 21:44:37)*

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 104,205

Hi Ritu;

Question should be asked in "Help Me."

The CAS all return

Which their pages claim is the principal value.

You can view it as the solutions to equation

Which has roots:

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,015

hi Ritu the question has already been answered by ganesh in post#5.

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Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

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