答：
(1-2*3^(-1))+(3-2*3^(-2))+`````+[(2n-1)-2*3^(-N)]
=(1+3+5+.+2n-1 ) + 2*[(1/3)^1+(1/3)^2+.+(1/3)^n ]
=(1+2n-1) n /2 +2* (1/3)* [1-(1/3)^n ]/ (1-1/3)
=n^2 +1-(1/3)^n
=n^2 -(1/3)^n +1
求和(1-2*3^(-1))+(3-2*3^(-2))+`````+[(2n-1)-2*3^(-N)]
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