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