lim(x-1)^2/(x^3+2x)
=0/3
=0
所以,(x-1)^2/(x^3+2x)是无穷小,
根据无穷小与无穷大的关系,
(x^3+2x)/(x-1)^2是无穷大
所以,
lim(x^3+2x)/(x-1)^2=∞