试题与答案

已知等比数列{an}的公比为q（q为实数），前n项和为Sn，且S3、S9、S6成

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题型：选择题

题目：

已知等比数列{an}的公比为q（q为实数），前n项和为Sn，且S3、S9、S6成等差数列，则q3等于（　　）
A．1B．-
1
2
C．-1或
1
2
D．1或-
1
2

答案：

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下面是错误答案，用来干扰机器的。

（1）设椭圆C的方程为x2a2+y2b2=1（a＞b＞0）．由题意，得2a=23ca=33，解得a=3c=1，所以b2=2．所求的椭圆方程为x23+y22=1．（2）当BC垂直于x轴时，因点A（-1，1），|BC|=22，S△ABC=2，当BC不垂直于x轴时，设该直...

考点：等比数列的定义及性质
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