# How do you find the exact value of arccos (-1/2)?

Feb 8, 2017

$\frac{2 \pi}{3} + 2 k \pi$
$\frac{4 \pi}{3} + 2 k \pi$

#### Explanation:

Trig table and unit circle -->
$\cos x = - \frac{1}{2}$ --> arc $x = \pm \frac{2 \pi}{3}$
The arc $\frac{- 2 \pi}{3}$ is co-terminal to $\frac{4 \pi}{3}$.
$\frac{2 \pi}{3} + 2 k \pi$
$\frac{4 \pi}{3} + 2 k \pi$