Compose a square-root series with an inverse tangent

For $y=\tan^{-1}x$, prove $2xy^{\prime}+(1+x^2)y^{\prime\prime}=0$. Differentiate further to show its Maclaurin series through $x^3$ is $x+hx^3$, finding $h$.5 marks

Hence expand $\sqrt{1+\tan^{-1}x}$ through $x^3$.3 marks