(i) Rewrite 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.

(ii) Solve the equation \(\cot \theta - 2 \tan \theta = \sin 2\theta\) for \(90^\circ < \theta < 180^\circ\).