在公差d不为零的等差数列{an}中,a1,a3,a9成等比数列,则
的值为_______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/09e151e8083936ff799a0f27c54704d9.png)
更新时间:2019-10-04 17:43:18
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