Đáp án:
Giải thích các bước giải:
`P=(\frac{\sqrt{x}}{3+\sqrt{x}}+\frac{9+x}{9-x}).(3\sqrt{x}-x)`
ĐK: `x \ge 0, x \ne 9`
`P=[\frac{\sqrt{x}(\sqrt{x}-3)}{(\sqrt{x}+3)(\sqrt{x}-3)}-\frac{9+x}{(\sqrt{x}-3)(\sqrt{x}+3)}].(3\sqrt{x}-x)`
`P=[\frac{x-3\sqrt{x}-9-x}{(\sqrt{x}-3)(\sqrt{x}+3)}].(3\sqrt{x}-x)`
`P=\frac{-3\sqrt{x}-9}{(\sqrt{x}-3)(\sqrt{x}+3)}.(3\sqrt{x}-x)`
`P=\frac{-3(\sqrt{x}+3)}{(\sqrt{x}-3)(\sqrt{x}+3)}.\frac{\sqrt{x}(3-\sqrt{x})}{1}`
`P=3\sqrt{x}`
