I can not get this. the left hand side simplifies to the right.

$\displaystyle -x^2(x^2+1)^{-3/2}+(x^2+1)^{-1/2} \Rightarrow (x^2+1)^{-3/2}$

I tried this but but then if I factor out (x^2+1) there are extra terms etc.

$\displaystyle -x^2(x^2+1)(x^2+1)^{-1/2}+(x^2+1)^{-1/2}=? $