第1个回答 2013-01-09
设m=1/2+1/3+1/4
（1+1/2+1/3+1/4）*（1/2+1/3+1/4+1/5）-（1+1/2+1/3+1/4+1/5）*（1/2+1/3+1/4）
=(1+m)*(m+1/5)-(1+m+1/5)*m
=m(1+m)+1/5(1+m)-[(1+m)*m+1/5*m]
=m(1+m)+1/5(1+m)-(1+m)*m-1/5*m
=1/5(1+m)-1/5*m
=1/5(1+m-m)
=1/5*1
=1/5本回答被网友采纳
（1+1/2+1/3+1/4）*（1/2+1/3+1/4+1/5）-（1+1/2+1/3+1/4+1/5）*（1/2+1/3+1/4）
=(1+m)*(m+1/5)-(1+m+1/5)*m
=m(1+m)+1/5(1+m)-[(1+m)*m+1/5*m]
=m(1+m)+1/5(1+m)-(1+m)*m-1/5*m
=1/5(1+m)-1/5*m
=1/5(1+m-m)
=1/5*1
=1/5本回答被网友采纳
第2个回答 2013-01-10
=(1+1/2+1/3+1/4)*(1+1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)=(1+1/2+1/3+1/4+1/5)*(1+1/2+1/3+1/4-1/2-1/3-1/4)-(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
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