第1个回答 2019-07-01
令U[n]=2^n n!/ n^n
则lim[n→∞]U[n+1]/U[n]
=lim 【2^(n+1) (n+1)!/ (n+1)^(n+1) 】/ 【2^n n!/ n^n】
=lim 2 [n/(n+1)]^n
=2 lim[x→+∞] [x/(x+1)]^x
=2 lim[x→+∞][1- 1/(x+1)]^[-(x+1) · (-x)/(x+1)]
=2 lim[x→+∞] e^[-1/(1+1/x)]
=2 e^[-1/(1+0)]
=2/e <1
故收敛本回答被提问者采纳