Помогите решить уравнение , срочно!!! необходимо упростить

Решите задачу:

$\frac{\cos\alpha-2\sin\alpha}{\sin\alpha+\cos\alpha}-\frac{2-\cos^2\alpha}{\cos2\alpha}=\\ \frac{\cos\alpha-2\sin\alpha}{\sin\alpha+\cos\alpha}-\frac{2\sin^2\alpha+2\cos^2\alpha-\cos^2\alpha}{\cos^2\alpha-\sin^2\alpha}=\\ =\frac{\cos\alpha-2\sin\alpha}{\sin\alpha+\cos\alpha}-\frac{2\sin^2\alpha+\cos^2\alpha}{(\cos\alpha-\sin\alpha)(\sin\alpha+\cos\alpha)}=\\ \frac{\cos^2-\sin\alpha\cos\alpha-2\sin\alpha\cos\alpha+2\sin^2\alpha-2+\cos^2\alpha}{\cos^2\alpha-\sin^2\alpha}=\\$
$\frac{2\cos^2\alpha+2\sin^2\alpha-2-3\sin\alpha\cos\alpha}{\cos2\alpha}=\frac{-\frac32\sin2\alpha}{\cos2\alpha}=-\frac32tg2\alpha$