0.5*0.5*0.5*（0.5-0.5）=0
0.5*0.5+0.5*0.5-0.5
（ 0.5- 0.5）* 0.5* 0.5 *0.5=0
(0.5+0.5+0.5)x(0.5-0.5)=0
(0.5*0.5)+(0.5*0.5)-0.5
