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

x2+y2
2
−xy的值.

∵x(x-1)-(x2-y)=-2,
∴x2-x-x2+y=-2,
∴x-y=2,

x2+y2
2
-xy=
x2+y2−2xy
2
=
(x−y)2
2
=2.