Giúp mình với làm ơn đó

`A = (\frac{1}{\sqrt{x} + 3} - \frac{4}{9 - x}).\frac{x - 4\sqrt{x} + 3}{x - 1}` $\text{(đkxđ:}$ `x >= 0; x \ne 9; x \ne 1)`

`A = [\frac{\sqrt{x} - 3}{(\sqrt{x} + 3)(\sqrt{x} - 3)} + \frac{4}{x - 9}].\frac{x - 3\sqrt{x} - \sqrt{x} + 3}{x - 1}`

`A = [\frac{\sqrt{x} - 3 + 4}{(\sqrt{x} + 3)(\sqrt{x} - 3)}].\frac{(\sqrt{x} - 1)(\sqrt{x} - 3)}{x - 1}`

`A = [\frac{\sqrt{x} + 1}{(\sqrt{x} + 3)(\sqrt{x} - 3)}].\frac{(\sqrt{x} - 1)(\sqrt{x} - 3)}{(\sqrt{x} - 1)(\sqrt{x} + 1)}`

`A = \frac{\sqrt{x} + 1}{(\sqrt{x} + 3)(\sqrt{x} - 3)}.\frac{\sqrt{x} - 3}{\sqrt{x} + 1}`

`A = \frac{1}{\sqrt{x} + 3}`

Vậy `A = \frac{1}{\sqrt{x} + 3}`.