Use a Product-To-Sum Formula to Convert the Expression to a Sum

Multiple Choice

Use a product-to-sum formula to convert the expression to a sum or difference. Simplify where possible. $\cos 47 ^ { \circ } \cos 43 ^ { \circ }$

A) $\frac { 1 } { 2 } \left( 1 + \sin 4 ^ { \circ } \right)$
B) $\sqrt { 2 } \cos 2 ^ { \circ }$
C) $\frac { 1 } { 2 } \cos 4 ^ { \circ }$
D) $- \frac { 1 } { 2 } \cos 4 ^ { \circ }$
E) $\frac { 1 } { 2 } \left( 1 - \sin 4 ^ { \circ } \right)$