Complete the Identity $\frac { \cos ( 3 \theta ) - \cos ( 9 \theta ) } { \cos ( 3 \theta ) + \cos ( 9 \theta ) } = ?$

Multiple Choice

Complete the identity.
- $\frac { \cos ( 3 \theta ) - \cos ( 9 \theta ) } { \cos ( 3 \theta ) + \cos ( 9 \theta ) } = ?$

A) 0
B) $\tan ( 3 \theta ) \tan ( 6 \theta )$
C) $\cot ( 6 \theta )$
D) $- \tan ( 6 \theta )$