Use the fact that the trigonometric functions are periodic to find the exact value of the expression. Do not use a calculator.
-$\cot 390 ^ { \circ }$
A) $\frac { \sqrt { 3 } } { 3 }$
B) $\sqrt { 3 }$
C) $- \frac { \sqrt { 3 } } { 3 }$
D) $- \sqrt { 3 }$

Question

Quizplus · Accepted Answer

The cotangent function has a period of 360°, so $\cot 390^\circ = \cot (360^\circ + 30^\circ) = \cot 30^\circ$. The exact value of $\cot 30^\circ$ is $\sqrt{3}$.

Use the Fact That the Trigonometric Functions Are Periodic to Find