Find the Exact Value of Each Expression, If It Is $\cos ^ { - 1 } \left( - \frac { 1 } { 2 } \right)$

Essay

Find the exact value of each expression, if it is defined.
(a) $\cos ^ { - 1 } \left( - \frac { 1 } { 2 } \right)$
(b) $\sin ^ { - 1 } \left( - \frac { \sqrt { 3 } } { 2 } \right)$
(c) $\tan ^ { - 1 } \left( - \frac { \sqrt { 3 } } { 3 } \right)$