Sn=4/3an-(1/3)*(2^(n+1))+2/3,
Sn-1=4/3a（n-1）-(1/3)*(2^n)+2/3,
相减得
an=4/3an-4/3a（n-1）-(1/3)*(2^n)
an=4a(n-1)+2^n
4an-1=4^2*a(n-2)+4*2^(n-1)
...
4^(n-2)a2=4^(n-1)*a1+4^(n-2)*2^2
以上叠加
an=4^(n-1)*a1+2^n+4*2^(n-1)+...+4^(n-2)*2^2
=2^(2n-1)+2^n*[2^（n-1）-1]
=2^(2n)-2^n
2)设Tn=(2^n)/Sn
Sn=4/3[2^(2n)-2^n]-(1/3)*(2^(n+1))+2/3
=4/3*2^(2n)-2^(n+1)+2/3
Tn=(2^n)/Sn
=1/[4/3*2^n-2+2/(3*2^n)]
=3/2*【1/（2^(n+1)+1/2^n-3）】
Tn<3/2n
放缩T1+T2+T3+…Tn
推荐
- 设数列an的前n项和Sn=4/3an-1/3*2n+1+2/3,n=1,2,3…….
- 若数列{an}的前n项和为Sn=2/3an+1/3，则数列{an}的通项公式是an=_．
- 数列an的前n项和Sn且满足Sn=4/3an-1/3*2^n+1+2/3
- 设数列{an}的前n项和Sn=4/3an-{(1/3)*2^n+1}+2/3
- 数列{an}的前n项和为Sn，Sn=1-2/3an，则an=_．
- 一环形线圈放在匀强磁场中，设第1s内磁感线垂直线圈平面（即垂直于纸面）向里，如图甲所示.若磁感应强度B随时间t变化的关系如图乙所示，那么第3s内线圈中感应电流的大小与其各处所受
- 英译中I dont know why i told this to you today,but hope you will not let any person eles knows
- 若|a^n|=½,|b|^n=3,求（ab）^2n的值
猜你喜欢
- 黑海是海吗
- A;shall we do the puzzle,mum?B;_________ .(1,Thank you 2.NO it's late 3.Great,we do 请问选几
- sin4/2009π等于多少 cos4次方x-sin4次方x+2sin4次方x
- 几句英语改句子!~~要快啊~~~
- 您好!我想问问,一个男的对女的说顺其自然,水到渠成,
- one group of the test-takers were found later to score higher on memory tests译文
- 一共有56个桃子,2个2个的装能装完吗?5个5个的呢?
- The chairs should be put _____.翻译