Use an Identity to Write the Expression as a Single $2 \cos ^ { 2 } 22.5 ^ { \circ } - 1$

Multiple Choice

Use an identity to write the expression as a single trigonometric function or as a single number.
- $2 \cos ^ { 2 } 22.5 ^ { \circ } - 1$

A) $\sqrt { 3 }$

B) $\frac { \sqrt { 2 } } { 4 }$

C) $\frac { \sqrt { 3 } } { 3 }$

D) $\frac { \sqrt { 2 } } { 2 }$