Express the Product as a Sum Containing Only Sines or Cosines

question 1

Multiple Choice

Express the product as a sum containing only sines or cosines.
- $\cos ( 2 \theta ) \cos ( 4 \theta )$

• A) \(\frac { 1 } { 2 } [ \cos ( 2 \theta ) + \cos ( 6 \theta ) ]\)
• B) \(\cos ^ { 2 } \left( 6 \theta ^ { 2 } \right)\)
• C) \(\frac { 1 } { 2 } [ \cos ( 6 \theta ) - \cos ( 2 \theta ) ]\)
• D) \(\frac { 1 } { 2 } [ \cos ( 6 \theta ) - \sin ( 2 \theta ) ]\)