Establish the Identity $$\cos ( x - y ) - \cos ( x + y ) = 2 \sin x \sin y$$

question 119

Essay

Establish the identity.
- $$\cos ( x - y ) - \cos ( x + y ) = 2 \sin x \sin y$$

---

Definitions:

Wechsler Intelligence Scale

A standardized test designed to measure human intelligence through various verbal and non-verbal tasks.

Thematic Apperception Test

A psychological projective test where individuals express their thoughts and feelings through stories they make up about ambiguous pictures.

Rorschach

A psychological test in which subjects' perceptions of inkblots are recorded and then analyzed using psychological interpretation, complex algorithms, or both.

MMPI

The Minnesota Multiphasic Personality Inventory, a comprehensive psychological test used to assess personality traits and psychopathology.