Đáp án:
Giải thích các bước giải:
`B=\frac{\sqrt{x}}{\sqrt{x}+3}+\frac{2\sqrt{x}}{\sqrt{x}-3}-\frac{3x+9}{x-9}`
`B=\frac{\sqrt{x}(\sqrt{x}-3)}{(\sqrt{x}-3)(\sqrt{x}+3)}+\frac{2\sqrt{x}(\sqrt{x}+3)}{(\sqrt{x}-3)(\sqrt{x}+3)}-\frac{3x+9}{(\sqrt{x}-3)(\sqrt{x}+3)}`
`B=\frac{x-3\sqrt{x}+2x+6\sqrt{x}-3x-9}{(\sqrt{x}-3)(\sqrt{x}+3)}`
`B=\frac{3\sqrt{x}-9}{(\sqrt{x}-3)(\sqrt{x}+3)}`
`B=\frac{3}{\sqrt{x}+3}`