(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+ ……+(1/19-1/20)的答案

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(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+……+(1/19-1/20)的答案(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+……+(1/19-1/20)的答案(1/2-1

(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+ ……+(1/19-1/20)的答案
(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+ ……+(1/19-1/20)的答案

(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+ ……+(1/19-1/20)的答案
1/2-1/3)+(1/3-1/4)+(1/4-1/5)+ ……+(1/19-1/20)的第二项-1/3与第三项+1/3抵消为0,依此类推,只剩下头尾1/2和-1/20,所以(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+ ……+(1/19-1/20=1/2-1/20=9/20