- (a) Prove
$$\frac { \cos 3 \theta } { \sin \theta } + \frac { \sin 3 \theta } { \cos \theta } \equiv 2 \cot 2 \theta \quad \theta \neq ( 90 n ) ^ { \circ } , n \in \mathbb { Z }$$
(b) Hence solve, for \(90 ^ { \circ } < \theta < 180 ^ { \circ }\), the equation
$$\frac { \cos 3 \theta } { \sin \theta } + \frac { \sin 3 \theta } { \cos \theta } = 4$$
giving any solutions to one decimal place.