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(1/2+1/3+1/4+1/5)*(1/3+1/4+1/5+1/6)-(1/2+1/3+1/4+1/5+1/6)*(1/3+1/4+1/5)
=(1/2+1/3+1/4+1/5)*(1/3+1/4+1/5+1/6)-
〔(1/2+1/3+1/4+1/5)+1/6〕*(1/3+1/4+1/5)
=(1/2+1/3+1/4+1/5)*(1/3+1/4+1/5+1/6)-
(1/2+1/3+1/4+1/5)*(1/3+1/4+1/5)-1/6*(1/3+1/4+1/5)
=(1/2+1/3+1/4+1/5)*(1/3+1/4+1/5+1/6-1/3-1/4-1/5)-1/6*(1/3+1/4+1/5)
=(1/2+1/3+1/4+1/5)*1/6-1/6*(1/3+1/4+1/5)
=1/6*(1/2+1/3+1/4+1/5-1/3-1/4-1/5)
=1/6*1/2
=1/12
=(1/2+1/3+1/4+1/5)*(1/3+1/4+1/5+1/6)-
〔(1/2+1/3+1/4+1/5)+1/6〕*(1/3+1/4+1/5)
=(1/2+1/3+1/4+1/5)*(1/3+1/4+1/5+1/6)-
(1/2+1/3+1/4+1/5)*(1/3+1/4+1/5)-1/6*(1/3+1/4+1/5)
=(1/2+1/3+1/4+1/5)*(1/3+1/4+1/5+1/6-1/3-1/4-1/5)-1/6*(1/3+1/4+1/5)
=(1/2+1/3+1/4+1/5)*1/6-1/6*(1/3+1/4+1/5)
=1/6*(1/2+1/3+1/4+1/5-1/3-1/4-1/5)
=1/6*1/2
=1/12
追答
后面一个同样的方法,提取相同的因数,然后就能消去一部分数据,答案其实很简单
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