设等比数列{an}的前n项和为Sn,已知a2=6,6a1+a3=30,求an和Sn.
已知等比数列{an}的前n项和为Sn,a1+a2=12,a2+a3=-6,
记等差数列{an}的前n项和为Sn,设S3=12,且2a1,a2,a3+1成等比数列,求Sn.
设数列an的前n项和为Sn,已知a1=1,a2=6,a3=11
等差数列{an}的前n项和为Sn,设S3=12,且2a1,a2,a3 1成等比数列,求Sn?
等差数列an的前n项和为Sn,设S3=122,且2a1.a2.,a3+1成等比数列,求Sn
在等比数列{an},其前n项和为Sn a1=2 a1+a2+a3=6 求{an}的通项公式an以及前n项和为Sn
1.已知等差数列{an}的前n项和为Sn,若S3=12,且2a1,a2,a3+1成等比数列求 Sn
设数列{an}是公比为正数的等比数列,a1=2,a3=a2+4,求数列{an}的前n项和Sn
设数列的前an的前n项和为Sn,Sn=2an-2^n(1)求a1,a2,a3(2)证明{an+1-2an}是等比数列(3
设数列an的前n项和为Sn,已知S1=1,Sn+1/Sn=n+c/n,且a1,a2,a3成等差数列
设数列{an}的前n项和为Sn,并且满足2Sn=an²+n,an>0.(1)求a1,a2,a3.(2)猜想{a
已知{an}是各项为正数的等比数列,且a1=1,a2+a3=6,求该数列前10项的和Sn.