.[x+y-1]²与√2x-y+4互为相反数
即有(x+y-1)^2+根号(2x-y+4)=0
所以有x+y-1=0,2x-y+4=0
解得x=-1,y=2
(1/2)^x-y=(1/2)^(-1)-2=2-2=0