Define displacement variable and periodic function.

(N/A) $1$. Displacement Variable: In the context of oscillatory motion,the displacement variable represents the change in position of an object from its mean (equilibrium) position at any given time $t$. It is typically denoted by $x(t)$ or $y(t)$.
$2$. Periodic Function: $A$ function is called periodic if it repeats its values at regular intervals of time. Mathematically,a function $f(t)$ is periodic if $f(t + T) = f(t)$ for all $t$,where $T$ is a positive constant known as the time period of the function.