\[ y'(x)=\frac {1}{2} \sqrt {a} \left (2 \sqrt {a x^4+8 y(x)}-\sqrt {a} x^3+2 x^3 \sqrt {a x^4+8 y(x)}+2 x^2 \sqrt {a x^4+8 y(x)}\right ) \] ✓ Mathematica : cpu = 0.492046 (sec), leaf count = 66
\[\left \{\left \{y(x)\to \frac {1}{72} a \left (-72 c_1 x^4-96 c_1 x^3-288 c_1 x+144 c_1^2+9 x^8+24 x^7+16 x^6+72 x^5+87 x^4+144 x^2\right )\right \}\right \}\]
✓ Maple : cpu = 0.452 (sec), leaf count = 38
\[ \left \{ {\frac {1}{4}\sqrt {a{x}^{4}+8\,y \left ( x \right ) }}-\sqrt {a} \left ( {\frac {{x}^{4}}{4}}+{\frac {{x}^{3}}{3}}+x \right ) -{\it \_C1}=0 \right \} \]