\[
\boxed{
{x}^{2}{\it d4y} \left( x \right) +6\,x{\frac {{\rm d}^{3}}{{\rm d}{x}^{3}}}y \left( x \right) +6\,{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left( x \right) -{\lambda}^{2}y \left( x \right) =0}
\]