Using a Sum or Difference Identity, Write the Following as an Expression

Multiple Choice

Using a sum or difference identity, write the following as an expression involving functions of x.
- $\sin 22.5 ^ { \circ } \cos 22.5 ^ { \circ }$

A) $\frac { \sqrt { 2 } } { 2 }$
B) $\sqrt { 3 }$
C) $\frac { \sqrt { 2 } } { 4 }$
D) $\frac { \sqrt { 3 } } { 3 }$