Find the exact value of the expression.
-$\cos \left( - 2130 ^ { \circ } \right)$
A) $\frac { \sqrt { 3 } } { 2 }$
B) $\frac { 1 } { 2 }$
C) $- \frac { 1 } { 2 }$
D) $- \frac { \sqrt { 3 } } { 2 }$

Question

Quizplus · Accepted Answer

The cosine function is periodic with a period of $360^\circ$, so $\cos(-2130^\circ) = \cos(-2130^\circ + 6 \times 360^\circ) = \cos(90^\circ) = \frac{\sqrt{3}}{2}$. This uses the fact that adding or subtracting full rotations (multiples of $360^\circ$) does not change the value of the trigonometric function.

Find the Exact Value of the Expression cos⁡(−2130∘)\cos \left( - 2130 ^ { \circ } \right)cos(−2130∘)

Find the Exact Value of the Expression $\cos \left( - 2130 ^ { \circ } \right)$