求极限lim n^2 (1-cos1/n) n→∞
问题描述：
求极限lim n^2 (1-cos1/n) n→∞
答
用等价无穷小代换:
(1-cosx)~x^2/2,x趋于0,
则1-cos1/n~(1/n)^2/2
则原式=limn^2[(1/n)^2/2]
=1/2