Finding the correct angle from inverse cosine?

Question

For my math homework, I have to find an angle of rotation, $\theta$, by cos $\theta$ = $-\sqrt3/2$. When I plug this into my calculator, I get 5$\pi$/6, but the correct answer is -5$\pi$/6. What is the procedure to find the correct angle.

Answer 1

You have to use the context to figure out which angle is called for. For both sine and cosine, there will be two angles with the given value.