绝对值数列看不懂…

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  • 考虑数列 {bn}:

    bn= an-2a'n+1' ,n=1,2,...2012;

    b2013 = a2013 -2a1

    设{an}前n项的和为Sn ,{bn}前n项的和为Tn

    T2013 = S2013 - 2S2013 =0

    又 |bn| = |b1| = p (p不小于0) n=1,2,...2013

    下面用反证法证明p=0 .

    若p非0 ,则p>0 ,bn各项均非0.

    设 {bn}前2013项中正项项数为 k1,负项项数为k2 ,有k1+k2 =2013

    0= T2013 = k1*p -k2*p =(k1-k2)p =(2013-2k2)p

    由于(2013-2k2)是奇数减偶数结果非0,故上式与p非0矛盾

    所以 p=0

    bn=0 ,n=1,2,...2013

    由 b2013 = a2013 -2a1=0 得 a2013 =2a1

    由 bn= an-2a'n+1'=0 ,n=1,2,...2012;

    得 a1 =2a2=4a3=...=[2^(2012)] a2013

    所以 a1= 2^(2012)] 2a1 = 2^(2013)] a1

    a1 =0 ,a2013=0

    由 an =2a'n+1' ( n=1,2,...2012)得 an=0 ( n=1,2,...2013)

    所以 a1=a2=...=a2013 =0