Show That the Equation Is Not an Identity by Finding $\cos 2 x + \cos 6 x = 2 \cos 4 x \cos x$

Multiple Choice

Show that the equation is not an identity by finding a value of x for which both sides are defined but not equal.
- $\cos 2 x + \cos 6 x = 2 \cos 4 x \cos x$

A) $\frac { \pi } { 4 }$
B) 0
C) $2 \pi$
D) $- 2 \pi$