Find the exact value of the expression.
-cos 210°
A) $- \frac { \sqrt { 3 } } { 2 }$
B) $\frac { \sqrt { 2 } } { 2 }$
C) $- \frac { \sqrt { 2 } } { 2 }$
D) $\frac { \sqrt { 3 } } { 2 }$

Question

Find the exact value of the expression.
-cos 210° 
A) $- \frac { \sqrt { 3 } } { 2 }$
B) $\frac { \sqrt { 2 } } { 2 }$
C) $- \frac { \sqrt { 2 } } { 2 }$
D) $\frac { \sqrt { 3 } } { 2 }$

Quizplus · Accepted Answer

The cosine of 210° can be found using the unit circle or cosine function properties. 210° is in the third quadrant where cosine values are negative. It corresponds to a reference angle of 30°. Therefore, $\cos(210°) = - \cos(30°) = - \frac { \sqrt { 3 } } { 2 }$.

Find the Exact Value of the Expression −32- \frac { \sqrt { 3 } } { 2 }−23​​

Find the Exact Value of the Expression $- \frac { \sqrt { 3 } } { 2 }$