1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72=?

1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72=?
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72=?

1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72=?
1/2+1/6+1/20+1/30+1/42+1/56+1/72
=1/1 ×2+1/2×3+1/3×4……+1/8×9
=（2-1）/1 ×2+（3-2）/2×3+（4-3）/3×4……+（9-8）/8×9
=1-1/2+1/2-1/3+1/3-1/4+……+1/8-1/9
=1-1/9
=8/9