Perform the indicated operations and simplify the result so there are no quotients.
-$$\cos 67 ^ { \circ } = \cos 13 ^ { \circ } \cos 54 ^ { \circ } - \sin 13 ^ { \circ } \sin 54 ^ { \circ }$$

Question

Quizplus · Accepted Answer

This equation is an application of the cosine of a sum formula, $\cos (A + B) = \cos A \cos B - \sin A \sin B$, where $A = 13^\circ$ and $B = 54^\circ$, so $A + B = 67^\circ$.

Perform the Indicated Operations and Simplify the Result So There cos⁡67∘=cos⁡13∘cos⁡54∘−sin⁡13∘sin⁡54∘\cos 67 ^ { \circ } = \cos 13 ^ { \circ } \cos 54 ^ { \circ } - \sin 13 ^ { \circ } \sin 54 ^ { \circ }cos67∘=cos13∘cos54∘−sin13∘sin54∘

Perform the Indicated Operations and Simplify the Result So There $\cos 67 ^ { \circ } = \cos 13 ^ { \circ } \cos 54 ^ { \circ } - \sin 13 ^ { \circ } \sin 54 ^ { \circ }$