数学简便计算题 快

问题描述:

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.  不知道正确吗。。。。。难道你没发现我把加号抄成减号了吗