一道分数巧算题

(1+1/2+1/3+1/4)x(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)x(1/2+1/3+1/4)
=1*(1/2+1/3+1/4+1/5)+(1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-1*(1/2+1/3+1/4)-(1/2+1/3+1/4+1/5)-(1/2+1/3+1/4)
=1*(1/2+1/3+1/4+1/5-1/2-1/3-1/4)+(1/2+1/3+1/4+1/5)*(1/2+1/3+1/4-1/2-1/3-1/4)
=1*1/5+0
=1/5
累死我了！！？！！？

吓？！貌似那里做过。
等我想一想。

原式＝（1/2+1/3+1/4+1/5）+(1/2+1/3+1/4)x(1/2+1/3+1/4+1/5)-[(1/2+1/3+1/4)+(1/2+1/3+1/4+1/5)x(1/2+1/3+1/4)]=1/5