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