Question

When $\cos x=1$, what does $x$ equal?

Answer 1

Period of the trigonometric function $\cos x$.

The function $\cos x$ has period $2\mathrm{\pi }$.

And $\cos \left(0\right)=1$

Thus, $\cos \left(2n\mathrm{\pi }\right)=1$, for any integer $n$.

Therefore, $x$ can be any integer multiple of $2\mathrm{\pi }$ , including $0$.