\[ \boxed { {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) -f \left ( x \right ) \left ( y \left ( x \right ) -g \left ( x \right ) \right ) \sqrt { \left ( y \left ( x \right ) -a \right ) \left ( y \left ( x \right ) -b \right ) }=0} \]
Mathematica: cpu = 2.972878 (sec), leaf count = 39 \[ \text {DSolve}\left [y'(x)-f(x) (y(x)-g(x)) \sqrt {(y(x)-a) (y(x)-b)}=0,y(x),x\right ] \]
Maple: cpu = 0.484 (sec), leaf count = 0 \[ \text {could not solve} \]