Find the Exact Value of the Trigonometric Function $\cos \left( \frac { 5 \pi } { 6 } \right)$

Multiple Choice

Find the exact value of the trigonometric function. Do not use a calculator or tables.
- $\cos \left( \frac { 5 \pi } { 6 } \right)$

A) $- \frac { \sqrt { 2 } } { 2 }$
B) $- \frac { 1 } { 2 }$
C) $- \frac { \sqrt { 3 } } { 2 }$
D) $\frac { \sqrt { 3 } } { 2 }$