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