# Chapter 22--Fourier Series: Fundamental Period, Frequency, and Angular Frequency

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## Period

Long long ago, in a high school class called trigonometry, we leaned about **periodic functions**. A periodic function is a function that repeats itself over and over for infinity. The **period** of the function is the distance of one iteration that is infinitely repeating.

A signal is periodic if, for some and all *t*,

<ref>Textbook, 22.1</ref>

The picture to the right shows the plot of the standard sine function whose period is . What the plot does not show is that the line keeps extending and repeating the bumps and valleys over the whole x axis, or . But wait! Can't the period also be or ? In fact it can. Because the graph of sin(x) repeats itself every units, the period of the function is actually where n is any whole number from zero to