已知x(x-1)-(x的2次方-y)=-2,求x的2次方+y的2次方/2-xy

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已知x(x-1)-(x的2次方-y)=-2,求x的2次方+y的2次方/2-xy
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已知x(x-1)-(x的2次方-y)=-2,求x的2次方+y的2次方/2-xy
已知x(x-1)-(x的2次方-y)=-2,求x的2次方+y的2次方/2-xy

已知x(x-1)-(x的2次方-y)=-2,求x的2次方+y的2次方/2-xy
x(x-1)-(x^2-y)=-2
x^2-x-x^2+y=-2
-x+y=-2
x-y=2
(x^2+y^2)/2-xy
=(x^2-2xy+y^2)/2
=(x-y)^2/2
=2^2/2
=4/2
=2


因为:x(x-1)-(x^2-y)=-2, 所以:x-y=2
所以:[(x^2+y^2)/2]-xy=(x^2-2xy+y^2)/2=(x-y)^2/2=4/2=2