在等差数列{a
n}中,公差d≠0,且a
1,a
3,a
7成等比例数列,则
=______.
人气:256 ℃ 时间:2019-11-23 10:16:51
解答
由题意可得
a32=a1a7,
故
(a1+2d)2=a1(a1+6d),
解之可得d=
,或d=0(舍去)
故
=
=
=
故答案为:
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