1/2+1/6+1/12+1/20+1/30+.1/380+1/420=

分类: 作业答案 • 2022-07-31 11:12:10

问题描述：

答

1/2+1/6+1/12+1/20+1/30+.1/380+1/420
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+.+1/19-1/20+1/20-1/21
=1-1/21
=20/21