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@@写个证明

Posted by 200593141 at 2008-01-07 18:31:40 on Problem 2601
In Reply To:直接推公式啊 Posted by:cactuslrd at 2007-09-18 01:35:47 
2*n*a1 = n*a0 + n*a1 - 2*n*c1;
2*(n-1)*a2 = (n-1)*a1 + (n-1)*a2 - 2*(n-1)*c2;
2*(n-2)*a3 = (n-2)*a2 + (n-2)*a3 - 2*(n-2)*c3;
...
...
2*2*an-1 = 2*an-2 + 2*an - 2*2*cn-1;
2*1*an = 1*an-1 + 1*an+1 - 2*1*cn;

左右求和 即可把 a2-an 消掉
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