Use the Addition Formulas for Sine and Cosine to Simplify $\cos \left( \theta - \frac { \pi } { 3 } \right) + \cos \left( \theta + \frac { \pi } { 3 } \right)$

Multiple Choice

Use the addition formulas for sine and cosine to simplify the expression. $\cos \left( \theta - \frac { \pi } { 3 } \right) + \cos \left( \theta + \frac { \pi } { 3 } \right)$

A) $\sqrt { 3 }$ $\cos \theta$
B) $\cos \theta$
C) $\frac { 1 } { 3 } \cos \theta$
D) 0
E) 3 $\cos \theta$