等差数列{an}的公差d≠0,且a5,a9,a15成等比数列,则公比为______.
人气:413 ℃ 时间:2019-08-20 16:40:58
解答
依题意可知(a
1+8d)
2=(a
1+4d)(a
1+14d),
整理得2a
1d=8d
2,解得4d=a
1,
∴q=
=
=
.
故答案为:
.
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