\[ g(x) f\left (x^2+y(x)^2\right )+y(x) y'(x)+x=0 \] ✓ Mathematica : cpu = 0.369098 (sec), leaf count = 95
\[\text {Solve}\left [\int _1^{y(x)}\left (\frac {K[2]}{f\left (x^2+K[2]^2\right )}-\int _1^x-\frac {2 K[1] K[2] f'\left (K[1]^2+K[2]^2\right )}{f\left (K[1]^2+K[2]^2\right )^2}dK[1]\right )dK[2]+\int _1^x\left (g(K[1])+\frac {K[1]}{f\left (K[1]^2+y(x)^2\right )}\right )dK[1]=c_1,y(x)\right ]\] ✓ Maple : cpu = 0.098 (sec), leaf count = 30
\[ \left \{ \int _{{\it \_b}}^{y \left ( x \right ) }\!{\frac {{\it \_a}}{f \left ( {{\it \_a}}^{2}+{x}^{2} \right ) }}\,{\rm d}{\it \_a}+\int \!g \left ( x \right ) \,{\rm d}x-{\it \_C1}=0 \right \} \]