1/2+1/6+1/12+1/20+...+1/9900=1-1/2+1/2-1/3+1/3-1/4+……+1/99-1/100=1-1/100=99/100
=1/1*1/2+1/2*1/3+1/3*1/4+.....+1/99*1/100=1*1-1/2+1/2-1/3+1/3-1/4+.....+1/99-1/100=1*1-1/100=99/100
答案99/100
