设sn是等差数列an的前n项和 a6/a3=10/7 则s11/s5=

来源：学生作业帮助网编辑：作业帮时间：2024/05/04 05:32:33

设sn是等差数列an的前n项和 a6/a3=10/7 则s11/s5=
设sn是等差数列an的前n项和 a6/a3=10/7 则s11/s5=

设sn是等差数列an的前n项和 a6/a3=10/7 则s11/s5=
a(n) = a + (n-1)d,
s(n) = na + n(n-1)d/2.
s(2n-1) = (2n-1)a + (2n-1)(n-1)d = (2n-1)[a + (n-1)d] = (2n-1)a(n),
s(11)/s(5) = 11a(6)/[5a(3)] = (11/5)[a(6)/a(3)] = (11/5)(10/7) = 22/7

设Sn为等差数列{an}的前n项和,已知a6+a70,那么Sn中最小的是设Sn为等差数列{an}的前N项和,已知 a6 +a70,那么Sn 中最小的是已知等差数列{an}中Sn是它的前n项和,设a6=2,S10=10 设sn是等差数列an的前n项和,若a6/a5=9/11,则S11/S9 设Sn是等差数列{An}前n项的和.若A6=A3+A8.则S9= 设sn是等差数列an的前n项和 a6/a3=10/7 则s11/s5= 设Sn是等差数列 an 的前n 项和,已知a2=3,a6=11,求S7. 设Sn是等差数列{an}的前n项和,已知a2=3,a6=11,则S7=? 设Sn是等差数列｛an｝的前n项和,已知a2=3,a6=11,则S7等于? 设Sn是等差数列(an)的前n项和,已知a2等于3,a6等于11,则S7等于设Sn为等差数列{An}的前n项和,求证：{Sn/n}是等差数列设等差数列{an}的前n项和为Sn,若a6=S3=12,则an=多少? 设等差数列{an}的前n项和为Sn,若a6=S3=12,则an=? 设Sn是等比数列an的前n项和S3.S9.S6成等差数列,求a3.a9.a6成等差数列设Sn是等比数列an的前n项和S3.S9.S6成等差数列,求a3.a9.a6成等差数列设Sn是等差数列{an}前n项和若a6/a3=2/3 则S11/S5= 1.设等差数列{An}的前n项和为Sn.若a1= -11,a4+a6= -6,则当Sn取最小值时,n等于（）A.6 B.7 C.8 D.92.设Sn是等差数列{An}的前n项和,若a4=9,S3=15,则数列{An}的通项an=( ) A.2n-3 B.2n-1 C.2n+1 D.2n+3 3.已知Sn为等差数列设{an}是公差不为0的等差数列,a1=2,a1、a3、a6成等比数列,求{an}的前n项和Sn的值