设等差数列{an}前n项和为Sn,a3=4.则S5=

设等差数列{an}前n项和为Sn,a3=4.则S5= 设等差数列{an}的前n项和为Sn,已知a3=11,S15*S16 设Sn为等差数列｛an｝的前n项和,S8=4a3,a7=-2,a9=? 设等差数列{An}的前n项和为Sn,若A5=5A3,则S9/S5=? 设等差数列{an}的前n项和为Sn,若a5=5a3,则S9/S5=? 设等差数列｛AN｝的前N项和为SN,若A5=5A3则S9/S5=?. 设等差数列an的前n项和为Sn,若a5=5a3,则S9/S5=? 设等差数列{an}的前n项和为sn,已知a3=5,s3=9 设等差数列{an}的前n项和为Sn,a3+a7+a11=6,则S13= 设等差数列{an}的前N项和为Sn,且a3+a5+a7=15,则S9=? 设Sn为等差数列an的前n项和.S8=4a3.a7=-2,则a9 设等差数列｛an｝前n项和为Sn,若a1=-9,a3+a5=-6 设等差数列{an}的前n项和为Sn,如果a3+a19=6,那么S21=? 设等差数列[an]的前n项和为Sn,若a5=5a3,则S9/S5等于多少? 设等差数列an 的前n项和为sn已知a3=12 S12>0 S13 设等差数列｛an｝的前n项和为Sn,已知a3=12,S12>0,S13 设等差数列{an}的前n项和为Sn,已知a3=11,S15>0,S16 设等差数列{an}的前n项和为Sn,已知a3=12,S12>0,S130,S13