Questions in inv-trig

Select	Question
	If ${{\tan }^{-1}}\frac{x-1}{x+1}+{{\tan }^{-1}}\frac{2x-1}{2x+1}={{\tan }^{-1}}\frac{23}{36},$then $x =$
	${{\tan }^{-1}}\frac{{{c}_{1}}x-y}{{{c}_{1}}y+x}+{{\tan }^{-1}}\frac{{{c}_{2}}-{{c}_{1}}}{1+{{c}_{2}}{{c}_{1}}}+$ ${{\tan }^{-1}}\frac{{{c}_{3}}-{{c}_{2}}}{1+{{c}_{3}}{{c}_{2}}}+...+{{\tan }^{-1}}\frac{1}{{{c}_{n}}}=$
	$\sin \left\{ {{\sin }^{-1}}\frac{1}{2}+{{\cos }^{-1}}\frac{1}{2} \right\}=$
	${{\sin }^{-1}}\frac{4}{5}+2{{\tan }^{-1}}\frac{1}{3}=$
	${{\sin }^{-1}}x+{{\cos }^{-1}}x$ is equal to
	${{\tan }^{-1}}\frac{1}{2}+{{\tan }^{-1}}\frac{1}{3} =$
	${{\tan }^{-1}}\left( \frac{1}{11} \right)+{{\tan }^{-1}}\left( \frac{2}{12} \right)=$
	If ${{\tan }^{-1}}x+2{{\cot }^{-1}}x=\frac{2\pi }{3},$then x =
	If ${{\sin }^{-1}}x+{{\cot }^{-1}}\left( \frac{1}{2} \right)=\frac{\pi }{2},$then x is
	If ${{\sin }^{-1}}a+{{\sin }^{-1}}b+{{\sin }^{-1}}c=\pi ,$ then the value of $a\sqrt{(1-{{a}^{2}})}+b\sqrt{(1-{{b}^{2}})}+c\sqrt{(1-{{c}^{2}})}$ will be