Use the Fundamental Identities to Simplify the Expression $2 \cos 8 x \cos 2 x$

Multiple Choice

Use the fundamental identities to simplify the expression.
- $2 \cos 8 x \cos 2 x$

A) $\sin 10 x + \sin 6 x$
B) $\cos 10 x + \cos 6 x$
C) $\cos 6 x - \cos 10 x$
D) $\frac { 1 } { 2 } ( \cos 10 x + \cos 6 x )$