CPM Homework Help : PC3 Problem 9-57

Evaluate each of the following trigonometric expressions exactly.

$\cos\left(\frac{11\pi}{12}\right)$
Step (a):
$\cos\left(\frac{3\pi}{12}+\frac{8\pi}{12}\right)$

$\csc\left(\frac{7\pi}{12}\right)$
Step (b):
$\frac{1}{\sin\left(\frac{7\pi}{12}\right)}$