方法一：lim(x→∞) (x²-5)/(x²-1)=lim(x→∞) [1-(5/x²)]/[1-(1/x²)] .分子分母同时除以x²=1方法二：定义法对∨ε＞0,要使|(x²-5)/(x²-1)-1|=|4/(x²-1)|...