Question

Solve : ${\cos }^{-1}\left(\cos \frac{7\pi }{6}\right)$

Answer 1

${\cos }^{-1}\cos \frac{7\pi }{6}$

$={\cos }^{-1}\cos (\pi +\frac{\pi }{6})$

$={\cos }^{-1}\cos (-\frac{\pi }{6})$

$={\cos }^{-1}\frac{\sqrt{3}}{2}$

$=\frac{\pi }{6}$