Q:

How to find a negative value for cosine function?

Can someone explain me how to find a negative value of a cosine function like how to find x if $$\cos x=-\sqrt3/2$$
I just don't understand how to do it? Please explain it to me

A:

Solve $\cos x=\frac{\sqrt 3}2$ and recall that $\cos(\pi-x)=-\cos x$.

