Question

Find the principle value of ${\cos }^{-1}(-\frac{1}{2})$

Answer 1

${\cos }^{-1}\left(\frac{-1}{2}\right)\Rightarrow {\cos }^{-1}\left(\cos (\frac{\pi }{2}+\frac{\pi }{6})\right)$

$\Rightarrow \frac{\pi }{2}+\frac{\pi }{6}=\frac{2\pi }{3}$

Hence, this is the answer.