$A=\dfrac{\sqrt{x}+15}{x-9}-\dfrac{x}{x-3\sqrt{x}}+\dfrac{2\sqrt{x}+5}{\sqrt{x}+3}$ ĐK: $x\neq9$
$A=\dfrac{\sqrt{x}+15}{(\sqrt{x}-3)(\sqrt{x}+3)}-\dfrac{x}{\sqrt{x}(\sqrt{x}-3)}+\dfrac{2\sqrt{x}+5}{\sqrt{x}+3}$
$A=\dfrac{\sqrt{x}+15}{(\sqrt{x}-3)(\sqrt{x}+3)}-\dfrac{\sqrt{x}(\sqrt{x}+3)}{(\sqrt{x}+3)(\sqrt{x}-3)}+\dfrac{(2\sqrt{x}+5)(\sqrt{x}-3)}{(\sqrt{x}+3)(\sqrt{x}+3)}$
$A=\dfrac{\sqrt{x}+15-x-3\sqrt{x}+2x-6\sqrt{x}+5\sqrt{x}-15}{(\sqrt{x}+3)(\sqrt{x}-3)}$
$A=\dfrac{-3\sqrt{x}+x}{(\sqrt{x}+3)(\sqrt{x}-3)}$
$A=\dfrac{\sqrt{x}(-3+\sqrt{x})}{(\sqrt{x}+3)(\sqrt{x}-3)}$
$A=\dfrac{\sqrt{x}}{\sqrt{x}+3}$
Vậy $A=\dfrac{\sqrt{x}}{\sqrt{x}+3}$ với $x\neq9$.
