摘要:18. 已知是等比数列.Sn是其前n项的和.a1.a7.a4成等差数列.求证:2S3.S6.S12-S6.成等比数列.
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(本小题满分12分)
设{an}是公差不为O的等差数列,Sn是其前n项和,已知,且
(1)求数列{an}的通项an
(2)求等比数列{bn}满足b1=S1 ,b2=, 求和Tn=a1b1+a2b2+…+anbn
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(本小题满分12分)
设{an}是公差不为O的等差数列,Sn是其前n项和,已知,且
(1)求数列{an}的通项an
(2)求等比数列{bn}满足b1=S1 ,b2=, 求和Tn=a1b1+a2b2+…+anbn