设P={x-y,x+y,xy},Q={x+y,x-y,0},若P=Q,求x,y的值.

网友回答

(x+y)2=11,
x2+2xy+y2=11 (1)
(x-y)2=7
x2-2xy+y2=7 (2)
(1)+(2)得
x2+2xy+y2+x2-2xy+y2=11+7
x2+y2=9
(1)-(2)得
x2+2xy+y2-x2+2xy-y2=11-7
4xy=4xy=1