∵15(3x+2y-4）^2 ≥ 0,7|x-2y+2| ≥ 0
又：7|x-2y+2|=-15(3x+2y-4）^2
∴15(3x+2y-4）^2 = 0,7|x-2y+2| = 0
3x+2y-4=0
x-2y+2=0
x=1/2,y=5/4
(x+y)^2=(1/2+5/2)^2=9