解题方法
1 . 判断正误(正确的写正确,错误的写错误)
(1)求等比数列
的前n项和时可直接套用公式
来求.( )
(2)首项为a的数列既是等差数列又是等比数列,则其前n项和为
.( )
(3)若某数列的前n项和公式为
,则此数列一定是等比数列.( )
(4)若数列
的前n项和
,则数列
不是等比数列.( )
(1)求等比数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fbdcb1e2554b4dc87359ba028c79c504.png)
(2)首项为a的数列既是等差数列又是等比数列,则其前n项和为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1750a296a35fd6a5ea68e982ae6fc975.png)
(3)若某数列的前n项和公式为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8dd95eaff081923ceeff6b74d62ccef8.png)
(4)若数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5a1d93da1921383b3932de3363f17184.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
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解题方法
2 . 判断正误(正确的填“正确”,错误的填“错误”)
(1)等差数列的前n项和一定是项数n的二次函数.( )
(2)若等差数列
的公差为d,前n项和为
.则
的公差为
.( )
(3)若数列
的前n项和
,则
不是等差数列.( )
(4)等差数列
的前n项和
,
可能是等差数列.( )
(1)等差数列的前n项和一定是项数n的二次函数.
(2)若等差数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4dea1dd4ffcb4cf0697ca43079f6a1f2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4c9823c2429d3867217d283dba4bf042.png)
(3)若数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c3d2dd8cb8712c7890b14cf5beedf17f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
(4)等差数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/846fa57d92d6ad44d6a0cafad1e71ed4.png)
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