Use the Sum-To-Product Formulas to Find the Exact Value of the Given

Multiple Choice

Use the sum-to-product formulas to find the exact value of the given expression.
$$\cos 150 ^ { \circ } - \cos 30 ^ { \circ }$$

A) 1
B) -1
C) $- \sqrt { 3 }$
D) $- \frac { \sqrt { 3 } } { 2 }$
E) 0