lim(x→0）ln(x+1)/x=lim(x→0）ln(x+1)^(1/x)
=lnlim(x+1)^(1/x) 极限和对数ln交换顺序,lim(x+1)^(1/x)在x趋于0时是重要极限=e
=lne=1
所以ln(x+1)~x等价无穷小量在x趋于0时.