lim{(x^2-2x+3)/(x^2+4x+5)] (x→∞) =lim{(x^2-2x+3)/(x^2+4x+5)] (x→∞) 分子分母同除以x的平方(x^2) =lim{(1-2/x+3/x^2)/(1+4/x+5/x^2)] (x→∞) =(1-0+0)/(1+0+0)=1