f(x)=(e^1/x-1)/(e^1/x+1)间断点x=0limf(x)=lim(e^1/x-1)/(e^1/x+1)=1x→0+limf(x)=lim(e^1/x-1)/(e^1/x+1)=(1-e^(-1/x))/(1+e^(-1/x))=-1x→0-x=0是f(x)的跳跃性间断点
x没有趋向于哪里，怎么求？
