1/2+1/6+1/12+1/20+1/30+1/40+1/42+1/56+1/72

1/2+1/6+1/12+1/20+1/30+1/40+1/42+1/56+1/72
1/2+1/6+1/12+1/20+1/30+1/40+1/42+1/56+1/72

1/2+1/6+1/12+1/20+1/30+1/40+1/42+1/56+1/72
=1-1/2+1/2-1/3+1/3-1/4+…＋1/7-1/8+1/8-1/9 =1-1/9 =8/9 怎么中间还有个1/40啊?题抄得对吧?如果有再加个1/40 这个题的规律是 1/2=1-1/2 1/6=1/2-1/3 …… 1/72=1/8-1/9