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