a(n+1)=2Sn+1--(1)
an=2S(n-1)+1--(2)
(1)-(2),得
a(n+1)-an=2Sn-2S(n-1)=2an
得a(n+1)=3an
所以{an}为等比数列,公比为3
an=3^(n-1)
前n项和记为sn,a1=1,an+1=2sn+1
前n项和记为sn,a1=1,an+1=2sn+1
求an
求an
数学人气:524 ℃时间:2020-05-08 15:32:45
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