3Q,怎么简便2/3+2/15+2/35+2/63+2/99+2/143+2/195+2/255+2/323+2/399

来源：学生作业帮编辑：百度作业网作业帮分类：数学作业时间：2024/06/14 14:04:57

3Q,怎么简便
2/3+2/15+2/35+2/63+2/99+2/143+2/195+2/255+2/323+2/399

2/(n-1)(n+1)=1/(n-1)-1/(n+1)
2/3+2/15+2/35+2/63+2/99+2/143+2/195+2/255+2/323+2/399
=1-1/3+1/3-1/5+1/5-1/7+-----------+1/19-1/21
=1-1/21
=20/21

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