12/1+20/1+30/1+42/1+56/1+72/+90/1 等于几?

分类: 作业答案 • 2021-12-19 16:35:22

问题描述：

答

1/12+1/20+1/30+..+1/90
=1/3-1/4+1/4-1/5+....1/9-1/10
=1/3-1/10
=7/30

答

1/12+1/20+1/30+1/42+1/56+1/72+1/90
=（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)
=1/3-1/10
=7/30