设{An}是等差数列,a3=12,S12>0,S13

设{an}是等差数列,a3=12,S12>0,S13 设{An}是等差数列,a3=12,S12>0,S13 设等差数列{an}的前n项和sn,已知a3=12,s12>0.s13 {an}成等差数列 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=12,S12>0,S13 设等差数列{an}的前n项和为Sn,已知a3=12,S12>0,S130,S13 设等差数列{an}的前n项的和为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,且S12>0,S13 设等差数列{an}的前n项和为Sn,若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s,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大于0 s13小于0 设等差数列{an}的前n项和为Sn,已知a3=12,S12>0,S13 高二数学必修五一章等差数列的一道题,设等差数列{an}的前n项和为Sn,已知a3=12,S12>0,S13 等差数列{an}的前n项和Sn已知a3=12,S12>0,S13 设等差数列的前n项和为Sn,a3=12,S12>0,S13 设等差数列前n项和Sn 已知a3=12 S12>0 S13