1.已知数列{an}的前n项和为Sn=12n-n∧2.求证{an}是等差数列

来源：学生作业帮编辑：作业帮分类：综合作业时间：2024/05/12 09:05:30

1.已知数列{an}的前n项和为Sn=12n-n∧2.求证{an}是等差数列
2.等差数列三个正数和为15.并且这三个数分别加上1.3.9后又是等比.求这三个数

1 an=Sn-S(n-1)=12n-n^2-[12(n-1)-(n-1)^2]=13-2n
an-a(n-1)=-2故an为等差数列
2 设这三个数为a1,a2,a3
a1+a3=2a2
a1+a2+a3=5
(a1+1)(a3+9)=(a2+3)^2
解得 a1=3
a2=5
a3=7

1.已知数列{an}的前n项和为Sn=12n-n∧2.求证{an}是等差数列已知数列{an}的前n项和为Sn=n^2-3n,求证：数列{an}是等差数列已知数列｛an｝的前n项和sn=n方+3n,求证数列{an}是等差数列高二超难数列题!已知数列an的前n项和为Sn=n平方-3n 求证数列an是等差数列已知数列{an}的前n项和为Sn,且满足an+2Sn*Sn-1=0,a1=1/2.求证：{1/Sn}是等差数列已知数列{an}的前n项和sn满足sn=an^2+bn,求证{an}是等差数列已知数列｛An｝的各项均为正数,前n项和为Sn,且满足2Sn=An²+n-4 1.求证｛An｝为等差数列高一数学问题：已知数列{An}的前n项和为Sn=n^2+3n,求证：数列{An}是等差数列. 设数列an的前n项和为Sn,a1=1,an=(Sn/n)+2(n-1)(n∈N*) 求证:数列an为等差数列, 已知数列{An}的前N项和Sn=4n2+3n,求证{An}是等差数列已知数列an其前n项和为Sn,且Sn=3n^2+5n,求证数列an是等差数列已知数列an前n项的和sn＝n²－9n求证an为等差数列