①an=(2an+1)*a(n+1)
→1/a(n+1)=(2an+1)/an=1/拆族an+2
故{1/an}为等差数列旅蠢弊
②档巧令bn=2^n/an=(2n-1)*2^n
Sn=1*2+3*2^2+……+(2n-1)*2^n
2Sn= 1*2^2+3*2^3+……+(2n-1)*2^(n+1)
故Sn=2Sn-Sn=-[2+2^3+2^4+…+2^(n+1)]+(2n-1)*2^(n+1)
=-2*[1-2^(n+1)]/(1-2)+4+(2n-1)*2^(n+1)
=6-2^(n+2)+(2n-1)*2^(n+1)
=6+(2n-3)*2^(n+1)
求采纳!
求采纳!
求采纳!
(Ⅰ)∵an+1+an⋅an+1−an=0,
∴an+1+an⋅an+1−anan⋅伍慎an+1=0,
∴1an+1−1an=1,(3分)
又1a1=1,
∴数旦雀列{1an}是以1为首项模橘早,1为公差的等差数列.
∴1an=1+(n−1)×1=n,an=1n.
(Ⅱ)由(Ⅰ)知2nan=n⋅2n.
Sn=1×21+2×22+…+n×2n.①
2Sn=1×22+2×23+…+n×2n+1.②
由①−②得−Sn=21+22+…+2n−n×2n+1.
∴Sn=(n−1)2n+1+2.