ln(1+e)-ln(1+1/e)也就是ln[(1+e)/(1+1/e)]而(1+e)/(1+1/e)刚好等于elne就等于1
ln(1+e)-ln(1+1/e)=ln[(1+e)/(1+1/e)]=ln{(1+e)/[(e+1)/e]}=lne=1
lnx-lny=ln(x/y)
