A.xul+(i-1)*n B.xul+i*n C.xul-i*n D.xul+(i+1)*n
A.-1 B.0 C.1 D.2
A.x=x+y y=y(tǒng)+x x=x+y B.x=x+y y=x-y x=x-y C.x=x+y y=y(tǒng)-x x=x-y D.x=x-y y=x-y x=y(tǒng)-x