Answer
$\cos \frac{-\pi}{6}=\frac{-\sqrt 3}{2}$
Work Step by Step
We are given $\cos \frac{-\pi}{6}$
$\cos \frac{-\pi}{6}=\cos \frac{\pi}{6}$
convert $\frac{\pi}{6}$ radians to degrees
$\frac{\pi}{6}=\frac{\pi}{6}(\frac{180^\circ}{\pi})$
$\frac{\pi}{6}=30^\circ$
$\cos \frac{\pi}{6}=(\cos 30^\circ)$
$\cos \frac{-\pi}{6}=-(\cos 30^\circ)$
$\cos 30^\circ=\frac{\sqrt 3}{2}$
so $\cos \frac{-\pi}{6}=\frac{-\sqrt 3}{2}$
