Find the Exact Value of the Expression $- \frac { \sqrt { 3 } } { 2 }$

Multiple Choice

Find the exact value of the expression.
-cos 210°

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