Find the Exact Value of the Expression $\frac { 1 } { 2 }$

Multiple Choice

Find the exact value of the expression.
-cos 45°

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