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2018-12-30 01:39:51

• 令an=(2n)²/(2n-1)(2n 1)=1/[1-(1/2n)][1 (1/2n)]=(1/2)*{[1-(1/2n)] [1 (1/2n)]}/[1-(1/2n)][1 (1/2n)]=(1/2)*{1/[1 (1/2n)]   1/[1-(1/2n)]}=(1/2)*[2n/(2n 1)   2n/(2n-1)]=(1/2)*{1-[1/(2n 1)] 1 [1/(2n-1)]}=1   (1/2)*[1/(2n-1) - 1/(2n 1)] Sn=a1 a2 ... an=1*n   (1/2)*[(1/1-1/3) (1/3 - 1/5) (1/5 - 1/7) . 1/(2n-1) - 1/(2n 1)]=n   (1/2)*[1 - 1/(2n 1) ]=n{1 [1/(2n 1)]}

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  2018-12-30 01:39:51

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