Express as a Product $\cos 9 \theta - \cos \theta$ A) $- 2 \sin ( 5 \theta ) \sin ( 4 \theta )$

Multiple Choice

Express as a product. $\cos 9 \theta - \cos \theta$

A) $- 2 \sin ( 5 \theta ) \sin ( 4 \theta )$
B) $- 2 \sin ( 10 \theta ) \sin ( 8 \theta )$
C) $2 \cos ( 5 \theta ) \cos ( 4 \theta )$
D) $2 \cos ( 4 \theta ) \sin ( 3 \theta )$
E) $- 2 \sin ( 4 \theta ) \cos ( 3 \theta )$