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