(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