Show That the Equation Is Not an Identity by Finding $$\frac { \sin 3 x + \sin 9 x } { \cos 9 x - \cos 3 x } = ?$$

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.
- $$\frac { \sin 3 x + \sin 9 x } { \cos 9 x - \cos 3 x } = ?$$

A) $- \cot 3 x$
B) $\tan 3 x + \tan 9 x$
C) $\cot 3 x$
D) $\tan 6 x$