已知x(x-1)-(x2-y)=-2,求x2+y22−xy的值.
问题描述:
已知x(x-1)-(x2-y)=-2,求
−xy的值.
x2+y2
2
答
∵x(x-1)-(x2-y)=-2,
∴x2-x-x2+y=-2,
∴x-y=2,
∴
-xy=
x2+y2
2
=
x2+y2−2xy 2
=2.(x−y)2
2