у'=((x^3)'*(2*x+4)-(x^3)*(2*x+4)')/(2*x+4)^2=
=(3*x^2*(2*x+4)-(x^3)*2)/(2*x+4)^2=(4*x^3+12*x^2)/(2*x+4)^2
у'=((x^3)'*(2*x+4)-(x^3)*(2*x+4)')/(2*x+4)^2=
=(3*x^2*(2*x+4)-(x^3)*2)/(2*x+4)^2=(4*x^3+12*x^2)/(2*x+4)^2