问题标题:
计算:1/1x2+1/2x3+1/3x4+1/4x5+……1/39x40
问题描述:

计算:1/1x2+1/2x3+1/3x4+1/4x5+……1/39x40

谷春林回答:
  1/1x2+1/2x3+1/3x4+1/4x5+……1/39x40   =1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+……+1/39-1/40   =1-1/40   =39/40
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