Why must the angle contain $\pi$ for $\cos$ be periodic?

1. Is cosine pi periodic?
2. Is Cospix periodic?
3. Is cos 2 2πt a periodic signal?

Is cosine pi periodic?

The cosine function is a trigonometric function that's called periodic.

Is Cospix periodic?

They consist of a pattern which repeats as we move along the x axis. We say that they are periodic.

Is cos 2 2πt a periodic signal?

It is. In general, a function defined on is periodic if we can find a value such that for every and . In this case we call the period of the function or signal. We often choose the value to be positive.