记等差数列
的前
项和为
.若
,
,则
( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fb334e165679c6cb500c994cffa47147.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dc71709255f5a5a4101afb6b55bcc10d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b11e2bf8d65c24fc845446a32d881bd4.png)
A.140 | B.70 | C.160 | D.80 |
更新时间:2024-06-18 12:49:21
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【推荐1】等差数列
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【推荐2】在等差数列
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【推荐2】某研究所计划建设n个实验室,从第1实验室到第n实验室的建设费用依次构成等差数列,已知第7实验室比第2实验室的建设费用多15万元,第3实验室和第6实验室的建设费用共为61万元.现在总共有建设费用438万元,则该研究所最多可以建设的实验室个数是( )
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