(d)
Given that, $y = \cos^{- 1}{\sqrt{1 - t^{2}} = \sin^{- 1}t}$
and $x = \sin^{- 1}{\left( 3t - 4t^{3} \right) = 3\sin^{- 1}t}$
On differentiating both w.r.t. $t$ respectively, we get
$\frac{dy}{dt} = \frac{1}{\sqrt{1 - t^{2}}}\ and\ \frac{dx}{dt} = \frac{3}{\sqrt{1 - t^{2}}}$
$\therefore\frac{dy}{dx} = \frac{\frac{dy}{dt}}{\frac{dx}{dt}} = \frac{\left( \frac{1}{\sqrt{1 - t^{2}}} \right)}{3\left( \frac{1}{\sqrt{1 - t^{2}}} \right)} \Rightarrow \frac{dy}{dx} = \frac{1}{3}$