\(A=\dfrac{x^2-2xy+y^2+2xy}{x-y}=\dfrac{\left(x-y\right)^2+2}{x-y}=x-y+\dfrac{2}{x-y}\ge2\sqrt{\dfrac{2\left(x-y\right)}{x-y}}=\sqrt{2}\)
\(A_{min}=\sqrt{2}\) khi \(\left(x;y\right)=\left(\dfrac{\sqrt{2}-\sqrt{6}}{2};-\dfrac{\sqrt{2}+\sqrt{6}}{2}\right);\left(\dfrac{\sqrt{6}+\sqrt{2}}{2};\dfrac{\sqrt{6}-\sqrt{2}}{2}\right)\)