Periodic Functions
The function $ f(t)=sin(t+T) $ is periodic, with a period of $ T=2\pi $. This means that for $ T=2n\pi $, n an integer, the function will be unchanged from when $ T=0 $.
An example of a periodic function f(t)=sin(t+T). The dashed red line represents adding various values of T from T=0 to T=2pi.
