#### Answer

a) Need to calculate the value of inverse trigonometric funtion .
$sec^{-1}(-\sqrt 2)=\frac{3\pi}{4}$
b) Need to calculate the value of inverse trigonometric funtion.
$sec^{-1}(\frac{2}{\sqrt 3})=(\frac{\pi}{6})$
c) Need to calculate the value of inverse trigonometric funtion.
$sec^{-1}(-2)=\frac{2\pi}{3}$