问题标题：
(1/5+1/7+1/9)*(1/7+1/9+1/11)-(1/7+1/9)*(1/5+1/7+1/9+1/11)要算式
问题描述：
(1/5+1/7+1/9)*(1/7+1/9+1/11)-(1/7+1/9)*(1/5+1/7+1/9+1/11)要算式
桂修文回答：
令A=1/5+1/7+1/9,A=1/7+1/9
原式=A*(B+1/11)-B*(A+1//11)
=AB+1/11A-AB-1/11B
=1/11(A-B)
=1/11*1/5
=1/55
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