1.已知递增的等差数列{an}满足a1=1,a3=a2^2-4,则an=?2.若等差数列的前6项和为23,前9项和为57
已知an为等差数列,且a2=-8,若等差数列bn满足b1=-8,b2=a1+a2+a3,求bn的前n项和Tn.
已知公差不为零的等差数列{an},若a1+a3=4,且a2,a3,a5成等比数列,则其前10项和S10为( )
设数列{an}的前n项和为Sn,满足2Sn=an+1-2^n+1+1,且a1,a2+5.a3成等差数列
等比数列{an}的前n项和为Sn,且4a1,2a2,a3成等差数列.若a1=1,则S4=( )
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
递增等差数列an满足a1=1,a1,a2,a3为等比数列.设bn=an+2的an次方,求数列bn的前n向和sn
1.已知{an}为等差数列,a1+a3+a5=105,a2+a4+a6=99.以Sn表示{an}的前n项和,则使得Sn达
20、已知正向等差数列{an}的前n项和为Sn,若S3=12,且2a1,a2,a3+1成等比数列.
已知正向等差数列{an}的前n项和为Sn,若S3=12,且2a1,a2,a3+1成等比数列.
已知等差数列{an}满足a1=3,a3=-1.(1)求{an}的通项an;(2)求{an}前n项和Sn的最大值
已知正数等差数列an满足a1+a6=a2(a3-1),公比为q的等比数列Bn的前n项和Sn满足2S1+S3=3S2,a1
已知数列{an}是等差数列,它的前n项和为Sn.a1+a2+a3=4,a3+a4+a5=10.求SN