极限问题（急）

题目

极限问题（急）
第一题：lim的x趋近于无穷大（x-1）/（x+1）的x次方
第二题：lim的x趋近于1 1/（x-1）减去2/（x的平方-1）

答案

(1)原式等于
lim[1-2/(x+1)]^{[-(x+1)/2]*[-2x/(x+1)]}
=lim{[1-2/(x+1)]^{[-(x+1)/2]}^[-2x/(x+1)]
=e^lim[-2x/(x+1)]
=e^{-2lim[x/(x+1)]}
=(1/e^2)^lim[1-1/(x+1)]
=1/e^2
(2)原式等于
lim[1/(x-1)-2/(x^2-1)]
=lim[(x+1)/(x^2-1)-2/(x^2-1)]
=lim{(x-1)/[(x+1)(x-1)]}
=lim1/(x+1)
=1/2