(a)
Given, $sec^{- 1}\sqrt{1 + x^{2}} + cosec^{- 1}\frac{\sqrt{1 + y^{2}}}{y} + \cot^{- 1}{\frac{1}{z} = \pi}$
$\therefore\ \tan^{- 1}{x + \tan^{- 1}{y + \tan^{- 1}{z = \pi}}}$
$\Rightarrow \ \ \ \tan^{- 1}{\left( \frac{x + y + z - xyz}{1 - xy - yz - zx} \right) = \pi}$
$\Rightarrow \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x + y + z = xyz$