`a) (x\sqrt{y}+y\sqrt{x})/\sqrt{xy}:1/(\sqrt{x}-\sqrt{y})` `(x>0;y>0;x\ney)`
`=(\sqrt{xy}(\sqrt{x}+\sqrt{y}))/\sqrt{xy}. (\sqrt{x}-\sqrt{y})`
`=(\sqrt{x}+\sqrt{y}).(\sqrt{x}-\sqrt{y})`
`=x-y` (Xem lại đề ạ)
`b) \sqrt{y}/(x-\sqrt{xy})+\sqrt{x}/(y-\sqrt{xy})` `(x>0;y>0;x\ney)`
`=\sqrt{y}/(\sqrt{x}(\sqrt{x}-\sqrt{y}))+\sqrt{x}/(-\sqrt{y}(\sqrt{x}-\sqrt{y}))`
`=(\sqrt{y}.\sqrt{y}-\sqrt{x}.\sqrt{y})/(\sqrt{xy}(\sqrt{x}-\sqrt{y}))`
`=(y-x)/(\sqrt{xy}(\sqrt{x}-\sqrt{y}))`
`=(-(\sqrt{x}+\sqrt{y})(\sqrt{x}-\sqrt{y}))/(\sqrt{xy}(\sqrt{x}-\sqrt{y}))`
`=-(\sqrt{x}+\sqrt{y})/\sqrt{xy}` (đpcm)
