Express the Sum or Difference as a Product of Sines $$\cos ( 10 \theta ) - \cos ( 4 \theta )$$

Multiple Choice

Express the sum or difference as a product of sines and/or cosines.
- $$\cos ( 10 \theta ) - \cos ( 4 \theta )$$

A) $2 \cos ( 3 \theta )$
B) $2 \cos ( 7 \theta ) \cos ( 3 \theta )$
C) $- 2 \sin ( 7 \theta ) \sin ( 3 \theta )$
D) $- 2 \cos ( 7 \theta ) \sin ( 3 \theta )$