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