设等差数列{an}的前n项和为Sn ,且S15>0,a8+a9
设等差数列{an}的前n项和为Sn ,且S15>0,a8+a9
设Sn为等差数列{an}的前n项和,若S15=90,则a8等于( )
等差数列中,a80,且a9>|a8|,Sn为数列的前n项和则s1,s2,...s15都小于0,s16s17,...都大于
已知等差数列{an}的前n项和为sn,且a5=15,s15>0,s16
设等差数列{an}的前n项和为Sn,若S3=9,S5=20,则a7+a8+a9=( )
设等差数列{an}的前n项和为Sn,若S3=9,S6=36,则a7+a8+a9=______.
设等差数列{an}的前n项和为Sn且a5+a9=-84,S3=-171
已知等差数列(an)的前n项和为Sn,且a3=5,S15=225,设bn=2^a n+2n,求数
设{an}为等差数列,Sn为数列{an}的前n项和,已知S7=7,S15=75,
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,
已知等差数列{an}的前n项和为Sn,且a3=3,S15=120.
知等差数列{an}的前n项和为Sn,且a3=5,S15=225.