a1,a3,a9成等比数列
a3^2=a1*a9
(a1+2d)^2=a1*(a1+8d)
解得a1=d
(a1+a3+a9)/(a2+a4+a10)=(3a1+10d)/(3a1+13d)=13d/16d=13/16
已知等差数列{an}的公差d不等于0且a1,a3,a9成等比数列,则看图
已知等差数列{an}的公差d不等于0且a1,a3,a9成等比数列,则看图
数学人气：870 ℃时间：2019-08-19 01:08:29
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