(a) Simplify : $\tan^{-1}\left(\frac{\cos 2x - \sin 2x}{\cos 2x + \sin 2x}\right)$, $0 < x < \frac{\pi}{4}$. OR (b) Evaluate : $\tan\left(\sin^{-1} 1 - \cos^{-1}\left$-\frac{1}{2}\right$\right)$