Question

根据上面的规律试着快速计算下题.

Answer 1

1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90

=1/2×3+1/3×4+1/4×5+1/5×6+1/6×7+1/7×8+1/8×9+1/9×10

=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9)+(1/9-1/10)

=1/2-1/10

=2/5