Show That the Equation Is Not an Identity by Finding $$\frac { \cos 10 x - \cos 4 x } { \sin 10 x + \sin 4 x } = \text { ? }$$

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.
- $$\frac { \cos 10 x - \cos 4 x } { \sin 10 x + \sin 4 x } = \text { ? }$$

A) $- \tan 3 x$
B) $\cot 4 x + \cot 10 x$
C) $2 \tan 7 x \tan 3 x$
D) $\tan 7 x$