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