Simplify the Expression $\cos ^ { 2 } 4 x - \sin ^ { 2 } 4 x$

Multiple Choice

Simplify the expression.
- $\cos ^ { 2 } 4 x - \sin ^ { 2 } 4 x$

A) $\cos 8 x$
B) $2 \sin 4 x$
C) $\frac { 1 } { 2 } \sin 16 x$
D) $\cos 4 x$