giúp tui bài 15 vssssssss

`bb{a.}` ĐKXĐ: $u;v \geqslant 0;u \ne v$

`A=(u-v)/(\sqrt{u}+\sqrt{v}) - (\sqrt{u^3}+\sqrt{v^3})/(u-v)`

`=((\sqrt{u}-\sqrt{v})(\sqrt{u}+\sqrt{v}))/(\sqrt{u}+\sqrt{v}) - ((\sqrt{u}+\sqrt{v})(u-\sqrt{uv}+v))/((\sqrt{u}-\sqrt{v})(\sqrt{u}+\sqrt{v}))`

`=(\sqrt{u}-\sqrt{v}) - (u-\sqrt{uv}+v)/(\sqrt{u}-\sqrt{v})`

`=((\sqrt{u}-\sqrt{v})(\sqrt{u}-\sqrt{v})-(u-\sqrt{uv}+v))/(\sqrt{u}-\sqrt{v})`

`=(u-\sqrt{uv}-\sqrt{uv}+v-u+\sqrt{uv}-v)/(\sqrt{u}-\sqrt{v})`

`=(-\sqrt{uv})/(\sqrt{u}-\sqrt{v})`

 `bb{b.}` ĐKXĐ: $u;v \geqslant 0;u \ne \dfrac{9}{4} v$

`B=(2u+\sqrt{uv}-3v)/(2u-5\sqrt{uv}+3v)`

`=(2u - 2\sqrt{uv}+3\sqrt{uv}-3v)/(2u-2\sqrt{uv}-3\sqrt{uv}+3v)`

`=(2\sqrt{u}(\sqrt{u}-\sqrt{v})+3\sqrt{v}(\sqrt{u}-\sqrt{v}))/(2 \sqrt{u}(\sqrt{u}-\sqrt{v})-3\sqrt{v}(\sqrt{u}-\sqrt{v}))`

`=((2\sqrt{u}+3\sqrt{v})(\sqrt{u}-\sqrt{v}))/((2\sqrt{u}-3\sqrt{v})(\sqrt{u}-\sqrt{v}))`

`=(2\sqrt{u}+3\sqrt{v})/(2\sqrt{u}-3\sqrt{v})`