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. $\cos \frac { 5 \pi } { 12 } \cos \frac { \pi } { 12 }$

A) 0
B) -1/4
C) -1/2
D) 1/4
E) 1/2