Use the Half-angle Formulas to find the exact value of the trigonometric function.
-$\cos 165 ^ { \circ }$
A) $\frac { 1 } { 2 } \sqrt { 2 + \sqrt { 3 } }$
B) $\frac { 1 } { 2 } \sqrt { 2 - \sqrt { 3 } }$
C) $- \frac { 1 } { 2 } \sqrt { 2 + \sqrt { 3 } }$
D) $- \frac { 1 } { 2 } \sqrt { 2 - \sqrt { 3 } }$

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The Answer of Use the Half-angle Formulas to find the exact value of the trigonometric function.
-$\cos 165 ^ { \circ }$
A) $\frac { 1 } { 2 } \sqrt { 2 + \sqrt { 3 } }$
B) $\frac { 1 } { 2 } \sqrt { 2 - \sqrt { 3 } }$
C) $- \frac { 1 } { 2 } \sqrt { 2 + \sqrt { 3 } }$
D) $- \frac { 1 } { 2 } \sqrt { 2 - \sqrt { 3 } }$

Use the Half-Angle Formulas to Find the Exact Value of the Trigonometric