Answer
Exact value of $\cos (-\frac{11\pi}{6}) = \frac{\sqrt 3}{2}$
Work Step by Step
To find exact value of $\cos (-\frac{11\pi}{6})$, let's find its reference angle first.
As $ -\frac{11\pi}{6}$ terminates in quadrant I -
The reference angle = $(-\frac{11\pi}{6}) + 2\pi$ = $\frac{\pi}{6}$
As $ (-\frac{11\pi}{6})$ terminates in quadrant I, its $\cos$ will be positive. Therefore by reference angle theorem-
$\cos (- \frac{11\pi}{6})$ = $\cos\frac{\pi}{6}$
= $\frac{\sqrt 3}{2}$
