---
title: Complex Number Plane
---

## Complex Numbers

The complex number plane expresses a complex number in graphical form. The complex number is an extension of the real number
line that adds an imaginary axis. This creates a two dimensional space with real and imaginary coordinates. 

Complex numbers take the form (a + bi) with the real part being "a" expressed on the x-axis and "b" expressed on the y-axis. See the
graph below.

<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/a/af/Complex_number_illustration.svg/183px-Complex_number_illustration.svg.png" />

A complex number that is on the x-axis is called purely real; while a complex number that is on the y-axis only is 
called purely imaginary. The x-axis or real number line includes all real numbers. Therefore, the set of all real numbers is actually 
a subset of the complex numbers. All real numbers, then are complex numbers who imaginary component is zero. 

## Complex Polar Coordinates

In polar form the cooordinates are the radius to the point in the complex plane and the angle from the x-axis. 

The radius[r] is found from the pythagorean formula applied to the real and imaginary componenets. 

r = sqrt(a^2 + b^2)

The angle for the polar coordinate is found from taking the inverse tangent of the real and imaginary coordinates.

@ = arctan(b/a) where x > 0
@ = arctan(b/a) + pi where x < 0
@ is undefined when x = 0

<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/6/69/Complex_conjugate_picture.svg/300px-Complex_conjugate_picture.svg.png" />

#### More Information
-[Wikipedia:Complex number](https://en.wikipedia.org/wiki/Complex_number)
-[Wolfram](http://mathworld.wolfram.com/ComplexNumber.html)