(a) Use the substitution \(u=1+x^{2}\) to find
\(\int \frac{x}{\sqrt{1+x^{2}}} \mathrm{~d} x\)
(b) Find the solution of the differential equation
\(x \frac{\mathrm{~d} y}{\mathrm{~d} x}-y=x^{2} \sinh ^{-1} x\)
given that \(y=1\) when \(x=1\). Give your answer in the form \(y=\mathrm{f}(x)\).