Question 3 - A-Level Maths

Express the equation \(\cot \theta - 2 \tan \theta = \sin 2 \theta\) in the form \(a \cos ^ { 4 } \theta + b \cos ^ { 2 } \theta + c = 0\), where \(a\), \(b\) and \(c\) are constants to be determined.
Hence solve the equation \(\cot \theta - 2 \tan \theta = \sin 2 \theta\) for \(90 ^ { \circ } < \theta < 180 ^ { \circ }\).