Questions in inv-trig

Select	Question
	${{\cot }^{-1}}\frac{3}{4}+{{\sin }^{-1}}\frac{5}{13}=$
	If ${{\cos }^{-1}}x+{{\cos }^{-1}}y+{{\cos }^{-1}}z=\pi $, then
	If ${{\tan }^{-1}}x-{{\tan }^{-1}}y={{\tan }^{-1}}A,$then $A =$
	If ${{\tan }^{-1}}x+{{\tan }^{-1}}y+{{\tan }^{-1}}z=\frac{\pi }{2},$then
	If ${{\tan }^{-1}}\frac{x-1}{x+2}+{{\tan }^{-1}}\frac{x+1}{x+2}=\frac{\pi }{4}$, then $x =$
	${{\cos }^{-1}}\sqrt{1-x}+{{\sin }^{-1}}\sqrt{1-x}=$
	$\cos \left[ 2{{\cos }^{-1}}\frac{1}{5}+{{\sin }^{-1}}\frac{1}{5} \right]=$
	${{\tan }^{-1}}\frac{a-b}{1+ab}+{{\tan }^{-1}}\frac{b-c}{1+bc}=$
	If ${{\tan }^{-1}}2x+{{\tan }^{-1}}3x=\frac{\pi }{4}$, then $x =$
	If ${{\cot }^{-1}}x+{{\tan }^{-1}}3=\frac{\pi }{2}$, then $x =$