# How do you evaluate arccost(-sqrt3 /2) ?

Jul 12, 2015

Find $\arccos t \left(\frac{- \sqrt{3}}{2}\right)$

#### Explanation:

Trig table gives ->

$\cos t = \left(- \frac{\sqrt{3}}{2}\right)$ --> arc $t = \frac{5 \pi}{6}$ or 150 deg

Trig unit circle gives another arc t that has the same cos value.

$t = - \frac{5 \pi}{6} \mathmr{and} \frac{7 \pi}{6}$

Answer: within period $\left(0 , 2 \pi\right)$, there are 2 answers: $\frac{5 \pi}{6} \mathmr{and} \frac{7 \pi}{6}$