\(A=\left(x-\dfrac{\sqrt{y\left(xy+\sqrt{y}\right)}}{\sqrt{x}+\sqrt{y}}\right)\cdot\dfrac{\sqrt{y}\cdot\sqrt{x}\left(\sqrt{y}-\sqrt{x}\right)-\sqrt{xy}\left(\sqrt{y}+\sqrt{x}\right)-\sqrt{xy\cdot y}}{\sqrt{xy}\left(y-x\right)}\)
\(=\dfrac{x\sqrt{x}+x\sqrt{y}-\sqrt{y\left(xy+\sqrt{y}\right)}}{\sqrt{x}+\sqrt{y}}\cdot\dfrac{\sqrt{xy}\left(y-x\right)}{\sqrt{xy}\left(-2\sqrt{x}-\sqrt{y}\right)}\)
\(=\dfrac{\left(\sqrt{x}-\sqrt{y}\right)\left(x\sqrt{x}+x\sqrt{y}-\sqrt{y\left(xy+\sqrt{y}\right)}\right)}{2\sqrt{x}+\sqrt{y}}\)