已知x(x-1)-(x2-y)=-3求x2+y2/2-xyx2是x的平方y2是y的平方x2+y2/2是二分之x2+y2
问题描述：
已知x(x-1)-(x2-y)=-3求x2+y2/2-xy
x2是x的平方
y2是y的平方
x2+y2/2是二分之x2+y2
答
x²-x-x²+y=3
-x+y=3
x-y=-3
(x²+y²)/2-xy
=(x²-2xy+y²)/2
=(x-y)²/2
=(-3)²/2
=9/2