应该是：
令（1+1/2+1/3+1/4)＝a，(1/2+1/3+1/4+1/5）＝b
原式＝ab－（a＋1/5)*(b-1/5)
=ab-(ab+1/5b-1/5a-1/25)
=ab-ab-1/5b+1/5a+1/25
=1/5(a+b)+1/25
=1/5*4/5+1/25
=4/25+1/25
=1/5
令（1+1/2+1/3+1/4)＝a，(1/2+1/3+1/4+1/5）＝b
原式＝ab－（a＋1/5)*(b-1/5)
=ab-(ab+1/5b-1/5a-1/25)
=ab-ab-1/5b+1/5a+1/25
=1/5(a+b)+1/25
=1/5*4/5+1/25
=4/25+1/25
=1/5
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第1个回答 推荐于2021-01-16
(1+1/2+1/3+1/4)×(1+1/2+1/3+1/4+1/5)－(1+1/2+1/3+1/4+1/5)×(1/2+1/3+1/4)
-(1+1/2+1/3+1/4)
=(1+1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)
=1/5本回答被提问者采纳
-(1+1/2+1/3+1/4)
=(1+1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)
=1/5本回答被提问者采纳
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