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# Periodic Function

A periodic function is a function that repeats its outputs at regular intervals, forming a definite pattern. The cycle of a periodic function is the shortest repeating portion of the graph, and the period is the horizontal length of one cycle.
More precisely, a function is said to be periodic if a non-zero constant exists such that and have the same value if and only if both and are in the domain.

Two well known examples of periodic functions are the trigonometric functions and both with a period of radians.

In the following applet, the graphs of and can be seen. Note that the domain of each function is in radians, not in degrees.