数列{an},a1=1,a(n+1)=2an-n^2+3n
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数列{an},a1=1,a(n+1)=2an-n^2+3n
1)是否存在常数λ,μ,使得数列{an+λn^2+μn}是等比数列,若存在,求出λ,μ的值,若不存在说明理由
1)是否存在常数λ,μ,使得数列{an+λn^2+μn}是等比数列,若存在,求出λ,μ的值,若不存在说明理由
a(n+1)=2an-n^2+3n=2an+(n+1)^2-(n+1)-2n^2+2n
将(n+1)^2-(n+1)移过去得a(n+1)-(n+1)^2+(n+1)=2(an-n^2+n)
再两边同除(an-n^2+n)得a(n+1)-(n+1)^2+(n+1)/(an-n^2+n)=2
所以当λ=-1,μ=1数列{an+λn^2+μn}是等比数列
将(n+1)^2-(n+1)移过去得a(n+1)-(n+1)^2+(n+1)=2(an-n^2+n)
再两边同除(an-n^2+n)得a(n+1)-(n+1)^2+(n+1)/(an-n^2+n)=2
所以当λ=-1,μ=1数列{an+λn^2+μn}是等比数列
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