根据e的定义:e=∑1/n! (n=0,1,2,....+∞)e=1/0! + 1/1! + 1/2! + 1/3! + 1/4! + 1/5! + .... =2.5 + 1/3! + 1/4! + 1/5! + .... < 2.5 + 1/3! + 1/(4x5) + 1/(5x6) + .... =2.5 + 1/3! + (1/4 -1/5) + (1/5-1/6) + .... < 2.5 + 1/6 + 1/4 < 3