The principal value of $\cos^{-1} \left( \cos \frac{13\pi}{6} \right)$ is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → $\frac{\pi}{6}$ ##
$\cos^{-1} \left( \cos \frac{13\pi}{6} \right) = \cos^{-1} \left( \cos \left( 2\pi + \frac{\pi}{6} \right) \right)$
$= \cos^{-1} \left( \cos \frac{\pi}{6} \right) = \frac{\pi}{6}$