设Sn为等差数列{An}的前n项和,已知S3=a7,a8-2a3=3 求an等于多少
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,已知a3=5,s3=9
设等差数列{an}的前n项和为Sn,已知a3=5,S3=9.
已知等差数列{An},前n项和为Sn.A3=6,S3=12.求数列{2^(n-1)An}的前n项和Bn.
等比数列{an}的前n项和为Sn,已知S1,S3,S2成等差数列,求{an}的公比Q.已知a1-a3=3,求sn?
设等差数列{an}的前n项和为Sn 已知a1+a7=16 a3+a4=14 求Sn
已知等差数列{An}的前n项和为Sn=2n²-10n,求(1)a1和a3的值;(2)求a5+a6+a7+a8;
已知等差数列{An}的前n项和为Sn,a1+a3+a6+a8=10求S8的值
已知等差数列{an}的前n项和为Sn,a3+a8=13,且S7=35.则a7=( )
设Sn为等差数列{an}的前n项和,S8=4a3,a7=-2,a9=?
已知等差数列an满足a3=7,a5+a7=26,an的前n项和为sn.1.求an和sn