Question

The value of ${\tan }^{-1}(-1)$ is

• A. ${45}^{\circ }$
• B. ${135}^{\circ }$
• C. $-{45}^{\circ }$
• D. $-{60}^{\circ }$

Answer 1

The correct option is C $-{45}^{\circ }$

${\tan }^{-1}(-1)=-{\tan }^{-1}\left(1\right)(\because {\tan }^{-1}(-x)=-{\tan }^{-1}x,x\in R)\Rightarrow {\tan }^{-1}(-1)=-{45}^{\circ }$