设等差数列{an}的前n项和为Sn,若1≤a4≤4,2≤a5≤3,S6取值范围是______.
设等差数列{an}的前n项和为Sn,若a4≥8,a5≤10,则S6的最小值为______.
设等差数列{an}(n∈正整数)的前n项和为Sn,该数列是单调递增数列,若S4≥10,S5≤15,则a4的取值范围
设Sn是等差数列An的前n项和,若S3/S6=1/3,则S6/S12等于
设等差数列{an}的前n项和为Sn,若S4≥10,S5≤15,则a4的最大值为______.
在等差数列{an}中,a2+a3=7,a4+a5+a6=18,求通项公式.设前n项和为sn,求1/s3+1/s6+...
设{an}是公比不等于1的等比数列,Sn是其前n项和,若a1,2a7,3a4成等差数列,求证12S3,S6,S12-S6
设等差数列{an}的前n项和为Sn,a3+a4=8,S7=5a5 (1)求an通项公式 (2)若b
设等差数列{an}的前n项和为Sn,a3 a4=8,S7=5a5(1)求an通项公式(2)若bn=
设等差数列{an}的前n项和为Sn,若a1=3,S6-S2=27.
设Sn是等比数列{an}的前n项和,S3,S9,S6成等差数列.
设等差数列{an}的首项及公差均是正整数,前n项和为Sn,且a1>1,a4>6,S3≤12,则a2015=______.
设Sn是等差数列『An』的前n项和,诺S3/S6=1/3,则S6/S12的值等于