已知x(x+1)-(x^2+y)=-3,求(x^2+y^2)/2-xy的值.

已知x(x+1)-(x^2+y)=-3,求(x^2+y^2)/2-xy的值.
已知x(x+1)-(x^2+y)=-3,求(x^2+y^2)/2-xy的值.

已知x(x+1)-(x^2+y)=-3,求(x^2+y^2)/2-xy的值.
x(x+1)-(x^2+y)=-3
x^2+x-x^2-y=-3
x-y=-3
(x^2+y^2)/2-xy
=(x^2+y^2-2xy)/2
=(x-y)^2/2
=(-3)^2/2
=9/2