已知x(x-1)-(x²-y)=-2,求二分之x²+y²-xy的值
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已知x(x-1)-(x²-y)=-2,求二分之x²+y²-xy的值
已知x(x-1)-(x²-y)=-2,求二分之x²+y²-xy的值
已知x(x-1)-(x²-y)=-2,求二分之x²+y²-xy的值
x(x-1)-(x²-y)=-2
→x-y=2.
∴(x²+y²)/2-xy
=(x²+y²-2xy)/2
=(x-y)²/2
=2²/2
=2.