Use the product-to-sum formulas to rewrite the product as a sum or difference. $$10 \cos 45 ^ { \circ } \cos 20 ^ { \circ }$$
A) $10 \left( \cos 25 ^ { \circ } + \cos 65 ^ { \circ } \right)$
B) $\cos 25 ^ { \circ } + \cos 65 ^ { \circ }$
C) $5 \left( \cos 65 ^ { \circ } - \cos 25 ^ { \circ } \right)$
D) $5 \left( \cos 25 ^ { \circ } + \cos 65 ^ { \circ } \right)$
E) $5 \left( \cos 65 ^ { \circ } + \sin 25 ^ { \circ } \right)$

Question

Use the product-to-sum formulas to rewrite the product as a sum or difference.​ $$10 \cos 45 ^ { \circ } \cos 20 ^ { \circ }$$ ​
A)​ $10 \left( \cos 25 ^ { \circ } + \cos 65 ^ { \circ } \right)$
B)​ $\cos 25 ^ { \circ } + \cos 65 ^ { \circ }$
C)​ $5 \left( \cos 65 ^ { \circ } - \cos 25 ^ { \circ } \right)$
D) $5 \left( \cos 25 ^ { \circ } + \cos 65 ^ { \circ } \right)$
E)​ $5 \left( \cos 65 ^ { \circ } + \sin 25 ^ { \circ } \right)$

Quizplus · Accepted Answer

The Answer is D

Use the Product-To-Sum Formulas to Rewrite the Product as a Sum