|x+3|≥0,(2x+y)^2≥0,|x+3|+(2x+y)^2=0,∴|x+3|=(2x+y)^2=0,∴x=-3,y=-2x=6∴3/4x²-(3y-1/4x²)+y = 3/4x²-3y+1/4x²+y = x²-2y = (-3)²-2*6 = -3