摘要:20.已知数列{an}满足an==2 an-1+2n-1(n∈N*.n2).且a4=81. (Ⅰ)求数列{an}的前三项a1.a2.a3的值,
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(本题12分)已知数列{an}中,a1=0,a2 =4,且an+2-3an+1+2an= 2n+1(),
数列{bn}满足bn=an+1-2an.
(Ⅰ)求证:数列{-
}是等比数列;
(Ⅱ)求数列{}的通项公式;
(Ⅲ)求.
(本题12分)已知数列{an}中,a1=0,a2
=4,且an+2-3an+1+2an= 2n+1(),
数列{bn}满足bn=an+1-2an.
(Ⅰ)求证:数列{-
}是等比数列;
(Ⅱ)求数列{}的通项公式;
(Ⅲ)求.
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