Evaluate Exactly $$\cos ^ { - 1 } \left( \cos \left( - \frac { \pi } { 6 } \right) \right)$$

Multiple Choice

Evaluate exactly.
- $$\cos ^ { - 1 } \left( \cos \left( - \frac { \pi } { 6 } \right) \right)$$

A) $\frac { 7 \pi } { 6 }$
B) $- \frac { 6 } { \pi }$
C) $\frac { \pi } { 6 }$
D) $- \frac { \pi } { 6 }$