Questions in inv-trig

Select	Question
	If ${{\cos }^{-1}}x-{{\cos }^{-1}}\frac{y}{2}=\alpha $, then $4{{x}^{2}}-4xy\cos \alpha +{{y}^{2}}$ is equal to
	If ${{\tan }^{-1}}x+{{\tan }^{-1}}y=\frac{\pi }{4}$ then
	If ${{\sin }^{-1}}(1-x)-2{{\sin }^{-1}}x=\pi /2$, then x equals
	If $\angle A={{90}^{o}}$ in the triangle ABC, then ${{\tan }^{-1}}\left( \frac{c}{a+b} \right)+{{\tan }^{-1}}\left( \frac{b}{a+c} \right)=$
	The solution of ${{\sin }^{-1}}x-{{\sin }^{-1}}2x=\pm \frac{\pi }{3}$ is
	For the equation ${{\cos }^{-1}}x+{{\cos }^{-1}}2x+\pi =0$, the number of real solution is
	$\sin \text{ }\left[ 3\,{{\sin }^{-1}}\left( \frac{1}{5} \right) \right]=$