小学六年级奥数（分数运算的技巧）二,7 - 知识问答

小学六年级奥数（分数运算的技巧）二,7

1个回答

设1/5+1/7+1/9+1/11=x 1/7+1/9+1/11=y
(1/5+1/7+1/9+1/11)*(1/7+1/9+1/11+1/13)-(1/5+1/7+1/9+1/11+1/13)*(1/7+1/9+1/11)
=x(y+1/13)-(x+1/13)y
=xy+x/13-xy-y/13
=x/13-y/13
=(x-y)/13
=1/5÷13
=1/65

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