Question
If $\frac{1+\sin^2\theta}{\sin^2\theta} + \frac{\cos^2\theta}{1+\cos^2\theta} + \frac{4\sin2\theta}{\sin^2\theta\cos^2\theta} = 4\sin2\theta - 1 = 0$ and $0 < \theta < \frac{\pi}{2}$, then $\cos4\theta = $
If $\frac{1+\sin^2\theta}{\sin^2\theta} + \frac{\cos^2\theta}{1+\cos^2\theta} + \frac{4\sin2\theta}{\sin^2\theta\cos^2\theta} = 4\sin2\theta - 1 = 0$ and $0 < \theta < \frac{\pi}{2}$, then $\cos4\theta = $