(i)[3]
Show that $\sin^2 2\theta (\cosec^2 \theta - \sec^2 \theta) = 4 \cos 2\theta$.
(ii(a))[4]
Hence solve for $0^\circ < \theta \leq 180^\circ$ the equation $\sin^2 2\theta (\cosec^2 \theta - \sec^2 \theta) = 3$.
(ii(b))[2]
Find the exact value of $\cosec^2 15^\circ - \sec^2 15^\circ$.