1.3x2-2xy-y2=0 (x-y)2-3(x-y)-18=02. x2+2xy+y2=4 (x-y)2+5x-5y=6
哪四个
1.x-y=0 x-y=0 3x+y=0 3x+y=0 x-y+3=0 x-y-6=0 x-y+3=0 x-y-6=02.x+y=2 x+y=2 x+y=-2 x+y=-2x-y-1=0 x-y+6=0 x-y-1=0 x-y+6=0