已知数列{an}的前n项和为Sn 若2(Sn+1)=3an则(a2+a5)/(a1+a4)=?
人气:255 ℃ 时间:2020-04-18 07:22:15
解答
2S(n+1)=3a(n)
2S(n)=3a(n-1)
2a(n)=3a(n)-3a(n-1)
a(n)=3a(n-1)
所以a(n)为公比为2的等比数列
(a2+a5)/(a1+a4)=a1*q*(1+q^3)/a1*(1+q^3)=q=3
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