已知{an}是公差为2的等差数列,且a1,a3,a4成等比数列,则数列{an}的前9项和等于( )
A. 0
B. 8
C. 144
D. 162
人气:237 ℃ 时间:2020-04-02 04:48:08
解答
由题意可得,
a32=a1a4∴
(a1+4)2=a1(a1+6)∴a
1=-8
∴
S9=9×(−8)+=0
故选A
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