求limx→+∞(x^2/x^2-1)^x的极值

来源:学生作业帮助网 编辑:作业帮 时间:2024/05/10 08:46:21
求limx→+∞(x^2/x^2-1)^x的极值

求limx→+∞(x^2/x^2-1)^x的极值
求limx→+∞(x^2/x^2-1)^x的极值

求limx→+∞(x^2/x^2-1)^x的极值
[x^2/(x^2-1)]^x
=[x/(x+1)]^x*[x/(x-1)]^x
=[1-1/(x+1)]^(x+1)*[1+1/(x-1)]^(x-1)*[1+1/(x-1)]/[1-1/(x+1)]
当n→+∞时,[1-1/(x+1)]^(x+1)=1/e
[1+1/(x-1)]^(x-1)=e
[1+1/(x-1)]/[1-1/(x+1)]=1
故limx→+∞[x^2/(x^2-1)]^x=1

因网上打字不便,下面将lim下的x→+∞省略
lim(x^2/x^2-1)^x
=lim[1+1/(x^2-1)]^x
=lime^(x*ln[1+1/(x^2-1)])
∵lim(x*ln[1+1/(x^2-1)])
=lim[x*1/(x^2-1)] 利用等价无穷小y→0时,ln(1+y)~y代换
=lim1/(x-1/x)]) ...

全部展开

因网上打字不便,下面将lim下的x→+∞省略
lim(x^2/x^2-1)^x
=lim[1+1/(x^2-1)]^x
=lime^(x*ln[1+1/(x^2-1)])
∵lim(x*ln[1+1/(x^2-1)])
=lim[x*1/(x^2-1)] 利用等价无穷小y→0时,ln(1+y)~y代换
=lim1/(x-1/x)]) 分子分母同除以x,分子为1,分母→+∞
=0
∴原极限=e^0=1

收起