Trigonometric Equation

$\left(1-\frac{\sin\theta}{\cos\theta}\right)(\sin^2\theta+ \cos^2\theta+2\sin\theta\cos\theta)=1+\frac{\sin\t heta}{\cos\theta}$

$\frac{(\cos\theta-\sin\theta)(\sin\theta+\cos\theta)^2}{\cos\theta}= \frac{\cos\theta+\sin\theta}{\cos\theta}$

$(\sin\theta+\cos\theta)(\cos^2\theta-\sin^2\theta-1)=0$

$(\sin\theta+\cos\theta)(\cos 2\theta-1)=0$

Then $\sin\theta+\cos\theta=0$

or $\cos 2\theta=1$

Can you continue?