Equation of SHM is a sine function of the form y = a sin(ωt-φ) , where y is displacement, a is amplitude,
ω is angular speed (=2πf, where f is frequency), t is time and φ is phase.
example : y = 10 sin(20 t - 0.75)
here 10 is amplitude, ω = 20 rad/s is angular speed , f = 20 / (2π) s-1 is frequency and 0.75 rad is phase.
Periodic functions are functions repeating with respect to time.
For example trignometric functions cos(kt), p sin(a t) + q cos(a t) etc
monotonically increasing or decreasing functions are non-periodic