Use the Formula for the Cosine of the Difference of Two Angles
-$\cos \left( 165 ^ { \circ } \right) \cos \left( 45 ^ { \circ } \right) + \sin \left( 165 ^ { \circ } \right) \sin \left( 45 ^ { \circ } \right)$
A) $\alpha = 165 ^ { \circ } , \beta = 45 ^ { \circ }$
B) $\alpha = - 165 ^ { \circ } , \beta = 45 ^ { \circ }$
C) $\alpha = - 45 ^ { \circ } , \beta = 165 ^ { \circ }$
D) $\alpha = 45 ^ { \circ } , \beta = 165 ^ { \circ }$

Question

Quizplus · Accepted Answer

The given expression is an application of the cosine difference identity, $\cos(\alpha - \beta) = \cos(\alpha)\cos(\beta) + \sin(\alpha)\sin(\beta)$, where $\alpha = 165^\circ$ and $\beta = 45^\circ$.