(y-1)/2=(1-2y)/4
2(y-1)=1-2y
2y-2=1-2y
2y+2y=1+2
4y=3
y=3/4 (3分之4) (y-1)/2=(1-2y)/4
2(y-1)=1-2y
2y-2=1-2y
2y+2y=1+2
4y=3
y=3/4 (3分之4)