\[
\boxed{
{\frac {\rm d}{{\rm d}x}}y \left( x \right) ={\frac {{x}^{3} \left( 3\,x+3+\sqrt {9\,{x}^{4}-4\, \left( y \left( x \right)  \right) ^{3}} \right) }{ \left( 1+x \right)  \left( y \left( x \right)  \right) ^{2}}}=0}
\]