sin x graph The zeros of f(x) = sin x are at the multiples of π. And it is there that the graph crosses the x-axis, because there sin x = 0 sin3x graph

Since the graph of g(X) = sin x has period 2π, then the constant a in

g(x)= sin 3x

indicates the number of periods in an interval of length 2π. (In y = sin x, a = 1.)