简单计算一下即可，答案如图所示
x y x+y y x+y x x+y x y =2(x+y) 2(x+y) 2(x+y) y x+y x x+y x y 1 1 1 =2(x+y) y x+y x x+y x y =2(x+y) 1 0 0 y x x-y x+y -y -x =2(x+y) x x-y -y -x =2(x+y) [-x^2+xy-y^2]
