Find the indefinite integral using trig substitution. $($Use $C$ for the constant of integration.$)$

${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{x^3}{\sqrt[\phantom{2}]{9-x^2}}$dxFind the indefinite integral using trig substitution. $($Use $C$ for the constant of integration.$)$

${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{x^3}{\sqrt[\phantom{2}]{9-x^2}}dx$