这是1^∞型未定式,利用重要极限lim(n→∞)(1+1/n)^n=elim(x→∞)(1-2/x)^(x/2-1)=lim(x→∞)(1-2/x)^[(-x/2)(x/2-1)(-2/x)]=lim(x→∞)[(1-2/x)^(-x/2)]^(2/x-1)=e^lim(x→∞)(2/x-1)=e^(-1)=1/e
