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已知数列{an}前n项和为Sn,求下列条件下数列的通项公式an.(1);(2)a1=2,a...
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已知数列{a
n}前n项和为S
n,求下列条件下数列的通项公式a
n.
(1)
![](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAE8AAAAgCAYAAABTliUJAAAAAXNSR0IArs4c6QAAAARnQU1BAACx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==
)
;
(2)a
1=2,a
n+1=a
n+3n+2;
(3)a
1=1,
![](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAH8AAAAjCAYAAAC98dWfAAAAAXNSR0IArs4c6QAAAARnQU1BAACx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)
;
(4)a
1=1,a
n+1=3a
n+2.
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