\[ y'(x)=\frac {x^2 \sqrt {4 a x-y(x)^2}+2 a}{y(x)} \] ✓ Mathematica : cpu = 1.43339 (sec), leaf count = 101
\[\left \{\left \{y(x)\to -\frac {\sqrt {147456 a^7 x-4096 a^6 x^6+128 a^3 e^{c_1} x^3-e^{2 c_1}}}{192 a^3}\right \},\left \{y(x)\to \frac {\sqrt {147456 a^7 x-4096 a^6 x^6+128 a^3 e^{c_1} x^3-e^{2 c_1}}}{192 a^3}\right \}\right \}\] ✓ Maple : cpu = 0.187 (sec), leaf count = 27
\[-\sqrt {-y \relax (x )^{2}+4 a x}-\frac {x^{3}}{3}-c_{1} = 0\]