Explain periodic function.

(N/A) periodic function is a function that repeats its values in regular intervals or periods.
In physics,periodic functions are used to represent periodic motion.
The simplest periodic functions are the sine and cosine functions.
Consider the function $f(t) = A \cos \omega t$.
The periodic time $T$ of this function is $T = \frac{2 \pi}{\omega}$,because when the argument $\omega t$ is increased by an integral multiple of $2 \pi$ radians,the value of the function remains the same.
Thus,the function $f(t)$ is periodic with period $T$,satisfying $f(t) = f(t + T)$.
Similarly,$f(t) = A \sin \omega t$ is a periodic function with the same period $T$.
$A$ linear combination of sine and cosine functions,$f(t) = A \sin \omega t + B \cos \omega t$,is also a periodic function with period $T$.
We can express this as $f(t) = D \sin(\omega t + \phi)$,where $D = \sqrt{A^2 + B^2}$ is the resultant amplitude and $\phi$ is the phase constant.