已知等差数列an的各项均为正数,观察程序框图,若n=3是,s=3 7

因为a2+a4=2a3,b2*b4=(b3)²所以2a3=b3,(b3)²=a3那么(b3)²=1/2*a3而b3>0,所以b3=1/2于是a3=1/4那么公差d=(1/

因为lga1,lga2,lga4成等差数列lga1+lga4=2lga2,lga1*a4=lg（a2）^2所以a1*a4=（a2）^2a1(a1+3d)=(a1+d)^2得a1=dan=ndBn=1/

结果是an=4(2n+1);首先由s1,s2,s3的关系可列出两个方程,关于a1,a2,a3.和已知的2a2=a1+a3联立,求出a1=4.接下来,利用根号sn是等差数列,推导出s（n）和a1的关系,

2S2=b2(a1+a2)=b1*q*(2a1+d)=32,b3S3=b3(a1+a2+a3)=b1*q²*(3a1+3d)=120,得d=2(都是正数）,q=2.∴an=a1+d(n-1)

（1）根据题意,设公差为d则a3=a1+2d=2d+1a9=a1+8d=8d+1有(2d+1)^2=8d+1d=1故通项：an=n（2）根据题意,设公比为q则b2=qb3=q^2有q-0.5q^2=0

因为2Sn=an^2+n-4,所以2S（n-1）=a（n-1）²+n-1-4.两式相减2an=an^2-a（n-1）²+1,a（n-1）²=an^2-2an+1=（an-

第一题：（1）∵a2=a1qa3=a1q²a4=a1q³又∵a2=2a1+33a2,a4,5a3成等差数列∴a1q=2a1+35a1q²+3a1q=2a1q³解

1.n=1时,2a1=2S1=a1²+1-4a1²-2a1-3=0(a1+1)(a1-3)=0a1=-1(数列各项均为正,舍去)或a1=3n≥2时,2an=2Sn-2S(n-1)=

sn=an(an+1)/2s(n-1)=a(n-1)(a(n-1)+1)/2两式相减an=an(an+1)/2-a(n-1)(a(n-1)+1)/2an^2-an-a^2(n-1)-a(n-1)=0(

n=1时,2a1=2S1=a1^2+1-4a1^2-2a1-3=0(a1+1)(a1-3)=0a1=-1(数列各项均为正,舍去)或a1=3n≥2时,2an=2Sn-2S(n-1)=an^2+n-4-a

可用递推法：2Sn=An+An*An递推2Sn-1=An-1+An-1*An-1两市相减,得：An+An-1=An*An-An-1*An-1因为An为正数,所以An-An-1=1之后求An,然后用求和

a1+a10=a2+a9=.a3+a8=10>=2更号下A3*A8A3*A8=25

∵{log2an}是公差为-1的等差数列∴log2an=log2a1-n+1∴an=2log2a1−n+1=a1•2−n+1∴S6=a1（1+12+…+132）=a1•1−1261−12=38，∴a1

首先需要计算出a(n)的通项loga1、loga2、loga3成等差数列,所以a(2)*a(2)=a(1)*a(3)(a(1)+d)^2=a(1)*(a(1)+2d)得：d=0所以a(n)=a(1)常

根号Sn的通项公式是nSn=n^2an=Sn-Sn-1=n^2-(n-1)^2=2n-1

log2A(n＋1)=log2An＋1=log2[2An],则：A(n＋1)=2An,则[A(n＋1)]/[An]=2=常数,则数列{An}是以A1=1为首项、以q=2为公比的等比数列,得：An=2^

Sn、an、1成等差,则2an=Sn＋1(n=1时,得a1=1),当n≥2时,有2a(n－1)=S(n－1)＋1,则2an－2a(n－1)=an,即an/[a(n－1)]=2=常数,所以{an}是等比

由题意知2an=Sn+1/2,an＞0,当n=1时,2a1=a1+1/2,解得a1=1/2,当n≥2时,Sn=2an-1/2,S(n-1)=2a(n-1)-1/2,两式相减得an=Sn-S(n-1)=

（1）由Sn，an，12成等差数列，可得2an＝Sn+12，∴a1＝12，a2=1（2）由2an＝Sn+12可得，2Sn=4an-1（n≥1），∴2Sn-1=4an-1-1（n≥2）∴两式相减得2an

由题意2an=Sn+1/2Sn=2an-1/2n=1时,S1=a1a1=2a1-1/2a1=1/2S(n+1)-Sn=a(n+1)2a(n+1)-1/2-[2an-1/2]=a(n+1)a(n+1)=