k=lim(x->∞) y/x=lim(x->∞)(x+1)^3/[x(x-1)^2]=1
b=lim(x->∞)(y-kx)=lim(x->∞) [(x+1)^3/(x-1)^2-x]=lim(x->∞)[(x^3+3x^2+3x+1)-x(x^2-2x+1)]/(x-1)^2
=lim(x->∞) [5x^2+2x+1]/(x-1)^2
=5
所以斜渐近线为y=x+5