1+1/(1+2)+1/(1+2+3)+·····+1/(1+2+3+·····+n) 求和

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1+1/(1+2)+1/(1+2+3)+·····+1/(1+2+3+·····+n)求和1+1/(1+2)+1/(1+2+3)+·····+1/(1+2+3+·····+n)求和1+1/(1+2)+

1+1/(1+2)+1/(1+2+3)+·····+1/(1+2+3+·····+n) 求和
1+1/(1+2)+1/(1+2+3)+·····+1/(1+2+3+·····+n) 求和

1+1/(1+2)+1/(1+2+3)+·····+1/(1+2+3+·····+n) 求和
1+2+3+…+n=n(n+1)/2 得1/(1+2+3+…+n)=2/n(n+1)=2/(1/n - 1/(n+1)) 故 1+1/(1+2)+1/(1+2+3)+……+1/(1+2+3+…+n) =2/(1/1 - 1/(1+1)) + 2/(1/2 - 1/(2+1))+...+2/(1/n - 1/(n+1)) =2/(1/1 - 1/(n+1)) =2n/(n+1)