# How do you evaluate cos^-1(1/2)?

${\cos}^{-} 1 \left(\frac{1}{2}\right) = \pm \frac{\pi}{3} \pm 2 \pi \cdot n \text{ }$where $n = 0 , 1 , 2 , 3 , \ldots .$
$\cos \left(\frac{\pi}{3}\right) = \frac{1}{2}$ and also
$\cos \left(- \frac{\pi}{3}\right) = \frac{1}{2}$
All co-terminal angles with $\frac{\pi}{3}$ and $- \frac{\pi}{3}$ have cosine function value$= \frac{1}{2}$