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