Difference between revisions of "Imaginary unit"

Revision as of 13:46, 26 October 2007

The imaginary unit, $i=\sqrt{-1}$ , is the fundamental component of all complex numbers. In fact, it is a complex number itself. It has a magnitude of 1, and can be written as $1 \mathrm{cis } \left(\frac{\pi}{2}\right)$ .

Trigonometric function cis

Main article: cis

The trigonometric function $\cis x$ (Error compiling LaTeX. Unknown error_msg) is also defined as $e^{ix}$ or $\sin x+i(\cos x)$ .

Series

When $i$ is used in an exponential series, it repeats at every fifth term:

$i^1=\sqrt{-1}$
$i^2=\sqrt{-1}\cdot\sqrt{-1}=-1$
$i^3=-1\cdot i=-i$
$i^4=-i\cdot i=-i^2=-(-1)=1$
$i^5=1\cdot i=i$

This has many useful properties.

Use in factorization

$i$ is often very helpful in factorization. For example, consider the difference of squares: $(a+b)(a-b)=a^2-b^2$ . With $i$ , it is possible to factor the otherwise-unfactorisable $a^2+b^2$ into $(a+bi)(a-bi)$ .

Problems

Introductory

Find the sum of $i^1+i^2+\ldots+i^{2006}$ (Source)

@@ Line 13: / Line 13: @@
 #<math>i^5=1\cdot i=i</math>
 This has many useful properties.
+==Use in factorization==
+<math>i</math> is often very helpful in factorization. For example, consider the difference of squares: <math>(a+b)(a-b)=a^2-b^2</math>. With <math>i</math>, it is possible to factor the otherwise-unfactorisable <math>a^2+b^2</math> into <math>(a+bi)(a-bi)</math>.
 ==Problems==
 === Introductory ===
@@ Line 22: / Line 25: @@
 * [[Complex numbers]]
 * [[Geometry]]
+* [[Omega]]
 [[Category:Constants]]

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