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