(u/v)`=(u`*v-u*v`)/v^2
u=2x^3+5
v=x^4+2x
y`=((2x^3+5)`*(x^4+2x)-(2x^3+5)*(x^4+2x)`)/(x^4+2x)^2=
=(6x^2*(x^4+2x)-(2x^3+5)*(4x^3+2))/(x^4+2x)^2=
=(6x^6+12x^3-8x^6-20x^3-4x^3-10)/(x^4+2x)^2=
=(-2x^6-12x^3-10)/(x^4+2x)^2= - 2*(x^6+6x^3+5)/(x^4+2x)^2