integrals.wolfram.com   Use one of Mathematica's 2500+ functions FREE online

Integrate[x^3/Sqrt[a^2 + x^2], x] ==
((-2*a^2 + x^2)*Sqrt[a^2 + x^2])/3

                3
               x
Integrate[-------------, x] == 
                2    2
          Sqrt[a  + x ]

     2    2        2    2
(-2 a  + x ) Sqrt[a  + x ]
--------------------------
            3