\[ \boxed { {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) =-1/2\,ax-b/2+x\sqrt {{a}^{2}{x}^{2}+2\,abx+{b}^{2}+4\,ay \left ( x \right ) -4\,c}=0} \]
Mathematica: cpu = 0.440556 (sec), leaf count = 60 \[ \left \{\left \{y(x)\to \frac {-4 a^2 c_1 x^2+4 a^2 c_1^2+a^2 x^4-a^2 x^2-2 a b x-b^2+4 c}{4 a}\right \}\right \} \]
Maple: cpu = 0.187 (sec), leaf count = 41 \[ \left \{ {\it \_C1}+a{x}^{2}+{\frac {a}{2}}-\sqrt {{a}^{2}{x}^{2}+2\,a bx+{b}^{2}+4\,ay \left ( x \right ) -4\,c}=0 \right \} \]