\[ \boxed { x{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) +f \left ( x \right ) \left ( \left ( y \left ( x \right ) \right ) ^{2}-{x}^{2} \right ) =0} \]
Mathematica: cpu = 20.763637 (sec), leaf count = 26 \[ \text {DSolve}\left [f(x) \left (y(x)^2-x^2\right )+x y'(x)=0,y(x),x\right ] \]
Maple: cpu = 0.093 (sec), leaf count = 0 \[ \text {could not solve} \]