==> \({(x + 1)^2} = A({x^2} + 1) + (Bx + C)\,x\)
==> \(A + B = 1\), \(C = 2\),\(A = 1\) ==> \(B=0\)
\({\sin ^{ - 1}}\left( {\frac{A}{C}} \right) = {\sin ^{ - 1}}\left( {\frac{1}{2}} \right) = 30^\circ = \frac{\pi }{6}\)