(2006•南京一模)设等差数列{an}的前n项的和是Sn,且a4+a8=0,则( )
设等差数列{an}的前n项和为Sn ,且S15>0,a8+a9
设Sn是等差数列{an}(n∈N+)的前n项和,且a1=1,a4=7,则S5=______.
在等差数列{an}中,已知sn是其前n项和,且a1一a4一a8一a12十a15=2,则s15=
设Sn为等差数列{an}的前n项和,若S15=90,则a8等于( )
设数列{an}是等差数列,a2=-6,a8=6,Sn是数列{an}的前n项和,则( )
设Sn是等差数列{an}的前n项和,已知3a4=7a7,且a1>0,当Sn取最大值时,求n!
设Sn是等差数列{an}的前n项和,S5=3(a2+a8),则a5a3的值为 ___ .
设等差数列{an}的前n项和为Sn,已知a4=12,且S8>0,S9
已知等差数列{an}的前n项和为Sn,若2a6=a8+6,则S7是( )
设数列(An)是等差数列,且a2=-6,a8=6,Sn是数列(An)的前n项和,求S4,S5,S6.
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)
设Sn是等差数列{an}的前n项和,若S7=35,则a4=______.