\[ f(x) y(x)-g(x)+y'(x)=0 \] ✓ Mathematica : cpu = 0.0188026 (sec), leaf count = 66
\[\left \{\left \{y(x)\to \exp \left (\int _1^x-f(K[1])dK[1]\right ) \int _1^x\exp \left (-\int _1^{K[2]}-f(K[1])dK[1]\right ) g(K[2])dK[2]+c_1 \exp \left (\int _1^x-f(K[1])dK[1]\right )\right \}\right \}\] ✓ Maple : cpu = 0.021 (sec), leaf count = 24
\[ \left \{ y \left ( x \right ) = \left ( \int \!g \left ( x \right ) {{\rm e}^{\int \!f \left ( x \right ) \,{\rm d}x}}\,{\rm d}x+{\it \_C1} \right ) {{\rm e}^{\int \!-f \left ( x \right ) \,{\rm d}x}} \right \} \]
\begin {equation} \frac {dy}{dx}+y\left ( x\right ) f\left ( x\right ) =g\left ( x\right ) \tag {1} \end {equation}
Integrating factor \(\mu =e^{\int f\left ( x\right ) dx}\). Therefore (1) becomes\[ \frac {d}{dx}\left ( e^{\int f\left ( x\right ) dx}y\left ( x\right ) \right ) =e^{\int f\left ( x\right ) dx}g\left ( x\right ) \] Integrating\begin {align*} e^{\int f\left ( x\right ) dx}y\left ( x\right ) & =\int e^{\int f\left ( x\right ) dx}g\left ( x\right ) dx+C\\ y\left ( x\right ) & =e^{-\int f\left ( x\right ) dx}\int e^{\int f\left ( x\right ) dx}g\left ( x\right ) dx+e^{-\int f\left ( x\right ) dx}C\\ & =\left ( \int e^{\int f\left ( x\right ) dx}g\left ( x\right ) dx+C\right ) e^{-\int f\left ( x\right ) dx} \end {align*}