1+2+3+。。。。+n=n（n+1）/21/(1+2+3+。。。。+n)=2/[n(n+1)]=2[1/n-1/(n+1)]所以，上式变为 2/[1/2-1/3+1/3-1/4+.....+1/99-1/100] =2/(1/2-1/100) =1-1/50 =0.98
99
