数学简便计算题 快(1/5+1/7+1/9)+(1/7+1/9+1/11)+(1/7+1/9)*(1/5+1/7+1/9+1/11)简便计算

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数学简便计算题 快(1/5+1/7+1/9)+(1/7+1/9+1/11)+(1/7+1/9)*(1/5+1/7+1/9+1/11)简便计算

数学简便计算题 快(1/5+1/7+1/9)+(1/7+1/9+1/11)+(1/7+1/9)*(1/5+1/7+1/9+1/11)简便计算
数学简便计算题 快
(1/5+1/7+1/9)+(1/7+1/9+1/11)+(1/7+1/9)*(1/5+1/7+1/9+1/11)
简便计算

数学简便计算题 快(1/5+1/7+1/9)+(1/7+1/9+1/11)+(1/7+1/9)*(1/5+1/7+1/9+1/11)简便计算
(1/5+1/7+1/9)*(1/7+1/9+1/11)-(1/7+1/9)*(1/5+1/7+1/9+1/11)
=(1/5+1/7+1/9)*(1/5+1/7+1/9+1/11)-(1/7+1/9)*(1/5+1/7+1/9+1/11)-1/5*(1/5+1/7+1/9)
=1/5*(1/5+1/7+1/9+1/11)-1/5*(1/5+1/7+1/9)
=1/5*1/11
=1/55.