2x−y+7=02 x-y+7=02x−y+7=0
2x+y+7=02 x+y+7=02x+y+7=0
x−2y+7=0x-2 y+7=0x−2y+7=0
x+2y+7=0x+2 y+7=0x+2y+7=0