(3-(x^2-x+1))/(x^3+1)=(-x^2+x+2)/(x^3+1)=-(x-2)(x+1)/((x+1)(x^2-x+1)=
=(2-x)/(x^2-x+1)
lim(2-x)/(x^2-x+1)=(2-(-1))/(1+1+1)=3/3=1
(3-(x^2-x+1))/(x^3+1)=(-x^2+x+2)/(x^3+1)=-(x-2)(x+1)/((x+1)(x^2-x+1)=
=(2-x)/(x^2-x+1)
lim(2-x)/(x^2-x+1)=(2-(-1))/(1+1+1)=3/3=1