Express the Product as a Sum Containing Only Sines or Cosines

Multiple Choice

Express the product as a sum containing only sines or cosines.
- $2 \cos ( 7 \theta ) \cos \theta$

A) $\cos ( 10 \theta ) + \sin ( 4 \theta )$
B) $\cos ( 14 \theta ) + \cos ( 2 \theta )$
C) $\cos ( 8 \theta ) + \cos ( 6 \theta )$
D) $\cos ( 8 \theta ) + \sin ( 6 \theta )$