a. Show that cos 2 = 5 sin may be written in the form a sin

a. Show that cos 2θ = 5 sin θ may be written in the form a sin² θ + b sin θ + c = 0, where a, b and c are constants to be found.

b. Hence solve, for −π < θ < π, the equation cos 2θ = 5 sin θ.