1. *,+,*2.-,*,-,**是乘号
1/4×1/4÷(1/4+1/4)=1/8(1/4+1/4)×(1/4+1/4)=1/4
1/4×1/4 +(1/4×1/4)=1/8(1/4+1/4)×(1/4+1/4)=1/4