Find the Exact Value of the Expression $\cos ^ { - 1 } \left( \sin \frac { 7 \pi } { 6 } \right)$

Multiple Choice

Find the exact value of the expression.
- $\cos ^ { - 1 } \left( \sin \frac { 7 \pi } { 6 } \right)$

A) $\frac { 2 \pi } { 3 }$
B) $\frac { 4 \pi } { 5 }$
C) $\frac { \pi } { 6 }$
D) $\frac { \pi } { 3 }$