Express the Product as a Sum Containing Only Sines or Cosines

question 168

Multiple Choice

Express the product as a sum containing only sines or cosines.
- $\cos ( 5 \theta ) \cos ( 4 \theta )$

• A) \(\frac { 1 } { 2 } [ \cos ( 9 \theta ) - \cos \theta ]\)
• B) \(\frac { 1 } { 2 } [ \cos \theta + \cos ( 9 \theta ) ]\)
• C) \(\cos ^ { 2 } \left( 20 \theta ^ { 2 } \right)\)
• D) \(\frac { 1 } { 2 } [ \cos ( 9 \theta ) - \sin \theta ]\)

---

Definitions:

Frugality

The quality of being economical with resources or expenditure; practicing restraint in the use of materials and funds.

Cognitive Dissonance

A psychological state of discomfort arising from holding two or more conflicting beliefs, values, or attitudes, leading to behavior change or attitude adjustment.

Consistency

is the tendency to maintain a uniform behavior, attitude, or belief over time.

Cognitions

Mental processes involved in gaining knowledge and comprehension, including thinking, knowing, remembering, judging, and problem-solving.