\[ y'(x)=\frac {x^3 \sqrt {4 a x-y(x)^2}+x^2 \sqrt {4 a x-y(x)^2}+\sqrt {4 a x-y(x)^2}+2 a}{y(x)} \] ✓ Mathematica : cpu = 4.46135 (sec), leaf count = 79
\[\left \{\left \{y(x)\to -\frac {1}{12} \sqrt {576 a x-\left (12 c_1+3 x^4+4 x^3+12 x\right ){}^2}\right \},\left \{y(x)\to \frac {1}{12} \sqrt {576 a x-\left (12 c_1+3 x^4+4 x^3+12 x\right ){}^2}\right \}\right \}\]
✓ Maple : cpu = 0.376 (sec), leaf count = 35
\[ \left \{ -\sqrt {- \left ( y \left ( x \right ) \right ) ^{2}+4\,ax}-{\frac {{x}^{4}}{4}}-{\frac {{x}^{3}}{3}}-x-{\it \_C1}=0 \right \} \]