y'(x)=\frac{2 a \left(4 a x-y(x)^2-1\right)}{128 a^4 x^3-96 a^3 x^2 y(x)^2+24 a^2 x y(x)^4-2 a y(x)^6+4 a x y(x)-y(x)^3-y(x)}