lim (e^1/x-e^-1/x）／（e^1/x＋e^-1/x) x趋向0+=lim (e^1/x-e^-1/x）*e^(1/x)／[（e^1/x＋e^-1/x)*e^(1/x)] x趋向0+=lim (e^2/x-1）／(e^2/x＋1) x趋向0+=lim (e^2/x+1-2）／(e^2/x＋1) x趋向0+=1-lim 2/(e^2/x+1) ...