设等差数列an的前n项和为Sn,且a4+a8>0,有下列四个结论:(1)S40
设等差数列{an}的前n项和为Sn ,且S15>0,a8+a9
等差数列{an}的前n项和Sn满足S20=S40,下列结论中一定正确的是( )
6、等差数列{an}前n项和为Sn,满足S20=S40,则下列结论中正确的是( D )
设数列{bn}的前n项和为Sn,且Sn=1-bn/2;数列{an}为等差数列,且a6=17,a8=23,
设等差数列{an}的前n项和为Sn,已知a4=12,且S8>0,S9
设等差数列{an}的前n项和为Sn,且a4-a2=8,S10=190,(1)求等差数列{an}的通项公式an
已知前n项和为Sn的等差数列{an}的公差不为零,且a2=3,又a4,a5,a8成等比数列
已知等差数列{an}的前n项和记为sn,如果a4=-12,a8=-4
设an公差不为0的等差数列.(1)前n项和为Sn,Sn=110,a1.a2.a4为等比数列.求an通项公式.
已知等差数列an满足a4=7,a3+a8=20,数列bn的前n项和为sn,且2sn=1-bn(n为正整数)
已知等差数列{an}满足a1=3.a4+a8=26,{an}的前n项和为Sn.求an及sn
设{an}的公比不为1的等比数列,其前n项和为sn,且a5,a3,a4成等差数列.