若x(x-1)-(x²-y)=-6,求(x²+y²)/2-xy的值

题目

若x(x-1)-(x²-y)=-6,求(x²+y²)/2-xy的值
若x(x-1)-(x²-y)=-6,求(x²+y²)/2-xy的值
若x(x-1)-(x²-y)=-6,求(x²+y²)/2-xy的值
若x(x-1)-(x²-y)=-6,求(x²+y²)/2-xy的值
若x(x-1)-(x²-y)=-6,求(x²+y²)/2-xy的值
若x(x-1)-(x²-y)=-6,求(x²+y²)/2-xy的值

答案

x(x-1)-(x²-y)=-6
得：x²-x-x²+y=-6
解得：x-y=6
所以（x-y）²=6²
x²-2xy+y²=36
所以x²+y²=36+2xy
（x²+y²)/2-xy
=(36+2xy)/2-xy
=18+xy-xy
=18