y'(x)=\frac{2 a x}{-128 a^4+96 a^3 x y(x)^2+32 a^3 x-24 a^2 x^2 y(x)^4-16 a^2 x^2 y(x)^2+2 a x^3 y(x)^6+2 a x^3 y(x)^4+2 a x^3-x^3 y(x)}