Question

What is the value of $\cot (-870^{\circ })$ ?

• A. $\sqrt{3}$
• B. $\frac{1}{\sqrt{3}}$
• C. $-\sqrt{3}$
• D. $-\frac{1}{\sqrt{3}}$

Answer 1

Answer: (A)

$\cot (-870^{\circ })=-\cot (2\times 360^{\circ }+150^{\circ })$
$=-\cot 150^{\circ }=-\cot (180^{\circ }-30^{\circ })$
$=\cot 30^{\circ }=\sqrt{3}$.