Solve: x+y=0,x−y=2x + y = 0, x - y = 2x+y=0,x−y=2.
(2,−2)(2, -2)(2,−2)
(1,1)(1, 1)(1,1)
(−1,1)(-1, 1)(−1,1)
(1,−1)(1, -1)(1,−1)