(a)
Let $I = \int_{}^{}\frac{\sin x\cos x}{\sqrt{1 - \sin^{4}x}}\ dx$
Put $\sin^{2}x = t \Rightarrow 2\sin x\cos x\ dx = dt$
$\therefore I = \int_{}^{}\frac{dt}{2\sqrt{1 - t^{2}}} = \frac{1}{2}\sin^{- 1}t + c$
$= \frac{1}{2}\sin^{- 1}{(\sin^{2}x)} + c$