\[
\boxed{
{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left( x \right) =-1/2\,{\frac { \left( {\frac {\rm d}{{\rm d}x}}f \left( x \right)  \right) {\frac {\rm d}{{\rm d}x}}y \left( x \right) }{f \left( x \right) }}-{\frac {g \left( x \right) y \left( x \right) }{f \left( x \right) }}=0}
\]