\[ y'(x)=x^2 \sqrt {a^2 x^2+2 a b x+4 a y(x)+b^2-4 c}-\frac {a x}{2}-\frac {b}{2} \] ✓ Mathematica : cpu = 0.778113 (sec), leaf count = 164
DSolve[Derivative[1][y][x] == -1/2*b - (a*x)/2 + x^2*Sqrt[b^2 - 4*c + 2*a*b*x + a^2*x^2 + 4*a*y[x]],y[x],x]
\[\text {Solve}\left [-\frac {\sqrt {a^2 x^2+2 a b x+4 a y(x)+b^2-4 c}}{2 a}-\frac {b \log \left (\sqrt {a^2 x^2+2 a b x+4 a y(x)+b^2-4 c}+a x+b\right )}{2 a}+\frac {b \tanh ^{-1}\left (\frac {2 a^2 x+2 a b}{2 a \sqrt {a^2 x^2+2 a b x+4 a y(x)+b^2-4 c}}\right )}{2 a}+\frac {b \log (4 a y(x)-4 c)}{4 a}+\frac {x^3}{3}=c_1,y(x)\right ]\] ✓ Maple : cpu = 0.329 (sec), leaf count = 39
dsolve(diff(y(x),x) = -1/2*a*x-1/2*b+x^2*(a^2*x^2+2*a*b*x+b^2+4*a*y(x)-4*c)^(1/2),y(x))
\[c_{1}+\frac {2 a \,x^{3}}{3}-\sqrt {a^{2} x^{2}+2 a b x +b^{2}+4 a y \left (x \right )-4 c} = 0\]