若x(y-1)-y(x-1)=4,则 x 2 + y 2 2 -xy=______

若x(y-1)-y(x-1)=4,则 x 2 + y 2 2 -xy=______.
2025-02-26 18:56:04
推荐回答(1个)
回答1:

∵x(y-1)-y(x-1)=4,
∴xy-x-yx+y=4,
∴-x+y=4,
∴x-y=-4,
x 2 + y 2
2
-xy,
=
x 2 + y 2 -2xy
2

=
(x-y ) 2
2

=
16
2

=8.