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Double Angle Identities

6. Trigonometric Identities and More Equations / Double Angle Identities / 문제 4

문제 4

Determine the exact value of the following expression by writing it as the cosine of a double angle.
cos² 112.5° - sin² 112.5°

A

(√2)/2

B

-1/2

C

-(√3)/2

D

-(√2)/2