Questions in inv-trig

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	${{\sin }^{-1}}\frac{1}{\sqrt{5}}+{{\cot }^{-1}}3$is equal to
	If ${{\cot }^{-1}}\alpha +{{\cot }^{-1}}\beta ={{\cot }^{-1}}x,$then $x=$
	If ${{\sin }^{-1}}\left( \frac{2a}{1+{{a}^{2}}} \right)+{{\sin }^{-1}}\left( \frac{2b}{1+{{b}^{2}}} \right)=2{{\tan }^{-1}}x,$then $x=$
	${{\cos }^{-1}}\frac{1}{2}+2{{\sin }^{-1}}\frac{1}{2}$is equal to
	${{\tan }^{-1}}\frac{3}{4}+{{\tan }^{-1}}\frac{3}{5}-{{\tan }^{-1}}\frac{8}{19}=$
	$4{{\tan }^{-1}}\frac{1}{5}-{{\tan }^{-1}}\frac{1}{70}+{{\tan }^{-1}}\frac{1}{99}=$
	If ${{\sin }^{-1}}x+{{\sin }^{-1}}y=\frac{2\pi }{3},$then ${{\cos }^{-1}}x+{{\cos }^{-1}}y=$
	${{\tan }^{-1}}\left( \frac{1}{4} \right)+{{\tan }^{-1}}\left( \frac{2}{9} \right)=$
	${{\tan }^{-1}}\left( \frac{x}{y} \right)-{{\tan }^{-1}}\,\left( \frac{x-y}{x+y} \right)$ is
	If ${{\sin }^{-1}}\frac{x}{5}+\text{cose}{{\text{c}}^{-1}}\left( \frac{5}{4} \right)=\frac{\pi }{2},$then $x=$