1x2分之1十2x3分之1十3x4分之l+4X5分之— 等于几？

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用裂项法
1x2分缓信之1十2x3分之1十3x4分之l+4X5分之—
=1-1/2+1/2-1/3+1/扰渗轮3-1/喊渗4+1/4-1/5
=1-1/5
=4/5

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1/2+2/散掘旅3+3/4+4/5
=30/冲凳60+40/散悄60+45/60+48/60
=163/60

4×1/5就已经4/5了 他算的不对

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1/2+2/3+3/4+4/5 = 163/60

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