1 . 如果
,那么![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e553e9312f9c3986ca947ff35d78b345.png)
_________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c82e33bcde20aa917f963bb2e0d34ab2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e553e9312f9c3986ca947ff35d78b345.png)
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2 . 由9个互不 相 等 的 正 数 组 成 的 数 阵
中,每 行 中 的 三 个 数 成 等 差 数 列,且
、
、
成等比数列,下列四个判断正确的有 (A )
①第2列
必成等比数列 ②第1列
不一定成等比数列
③
④若9个数之和等于9,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/723e56d3ef93429ebb95d55dceb7080a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c3ac40ade1fac57351ff631aa530398e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/eeb9d1aa1cc02e6fe13141ecf5f2549b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6bab5310774cd482fffd19586983b44c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/699f39dd97b907f10708e0dc75076f8a.png)
①第2列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ff7f8dbd52620255fae2cbd9c74543e4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b871fc1749d2960a23cf40524af8a0fc.png)
③
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/93a483f03e2a7fd4769bc50f184692d3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/723e56d3ef93429ebb95d55dceb7080a.png)
A.4个 | B.3个 | C.2个 | D.1个 |
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3 . 已知数列
的前
项和
,则其通项公式为
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041506963456/STEM/df6189f6548b4d3f8e345eeacf58895f.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041506963456/STEM/5c2ffb58e9be461bb4ea50204b4807f8.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041506963456/STEM/6f0dcbd135c04908b23ba05dac06736c.png)
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