设等差数列{an}的前n项和为Sn,已知a3=5,S3=9.
设等差数列{an}的前n项和为Sn,已知a3=5,S3=9.
设等差数列{an}的前n项和为sn,已知a3=5,s3=9
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.
已知等差数列{an}的前n项和为Sn,公差d≠0,且S3=9,a1,a3,a7成等比数列.
设等差数列{an}的前n项和为Sn,已知a3=4,S3=9,令bn=1/an(an+1)求数列bn的前10项和
已知等差数列{An},前n项和为Sn.A3=6,S3=12.求数列{2^(n-1)An}的前n项和Bn.
设等差数列{an}的前n项和为Sn,且a5+a13=34,S3=9.
等比数列{an}的前n项和为Sn,已知S1,S3,S2成等差数列,求{an}的公比Q.已知a1-a3=3,求sn?
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
已知数列{An}是等差数列前n项和Sn,A3=6,S3=12.
设等差数列{an}的前n项和为Sn 已知S3=S12 则当公差d