Question

${\cos }^{-1}\left(\cos \frac{7\pi }{6}\right)$ is equal to

• A. $\frac{7\pi }{6}$
• B. $\frac{5\pi }{6}$
• C. $\frac{\pi }{3}$
• D. $\frac{\pi }{6}$

Answer 1

Answer: (B)

${\cos }^{-1}\left(\cos \frac{7\pi }{6}\right)={\cos }^{-1}\left(\frac{-\sqrt{3}}{2}\right)$
$=\pi -{\cos }^{-1}\frac{\sqrt{3}}{2}=\pi -\frac{\pi }{6}=\frac{5\pi }{6}$.