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