询问一题数学因式分解的解答题先化解再求值X（X-1)-(X^2-Y)=-2求2份之一（X^2+Y^2)-XY的值

Question

询问一题数学因式分解的解答题
先化解再求值 X（X-1)-(X^2-Y)= -2 求 2份之一（X^2+Y^2)-XY 的值

Answer 1

X（X-1)-(X^2-Y)= -2
X^2-X-X^2+Y=-2
Y-X=-2
X-Y=2
(X^2+Y^2)/2-XY
=(X^2-2XY+Y^2)/2
=(X-Y)^2/2
=2^2/2
=2