2 solutions for, solve $\cos x = -1/2$? Answer sheet displays only one, does this mean there is only one? $\cos x = -1/2$ can occur in quadrants 2 or 3, that gives it 2 answers, however the answer sheet only shows one. Does this mean im doing something completely wrong, or are they just not showing the other one?
Thanks :D

It depends upon the range answers are allowed in.  If you allow $[0,2\pi)$, there are certainly two answers as you say:$\frac{2\pi}{3}$ and $\frac{4\pi}{3}$.  The range of arccos is often restricted to $[0,\pi)$ so there is a unique value.  If $x$ can be any real, then you have an infinite number of solutions:  $\frac{2\pi}{3}+2k\pi$ or $\frac{-2\pi}{3}+2k\pi$ for any integer $k$.
