Use the Formula for the Cosine of the Difference of Two

Multiple Choice

Use the Formula for the Cosine of the Difference of Two Angles
- $\cos \left( 155 ^ { \circ } \right) \cos \left( 35 ^ { \circ } \right) + \sin \left( 155 ^ { \circ } \right) \sin \left( 35 ^ { \circ } \right)$

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