\(A=\dfrac{\sqrt{x}+1}{\sqrt{x}-3}-\dfrac{7\sqrt{x}+3}{x-9}\\ A=\dfrac{\left(\sqrt{x}+1\right)\left(\sqrt{x}+3\right)-7\sqrt{x}-3}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\\ A=\dfrac{x+4\sqrt{x}+3-7\sqrt{x}-3}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\\ A=\dfrac{x-3\sqrt{x}}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\\ A=\dfrac{\sqrt{x}\left(\sqrt{x}-3\right)}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\\ A=\dfrac{\sqrt{x}}{\sqrt{x}+3}\)
`A=(sqrtx+1)/(sqrtx-3)-(7sqrtx+3)/(x-9)`
`đk:x>=0,x ne 9`
`A=((sqrtx+1)(sqrtx+3)-7sqrtx-3)/((sqrtx-3)(sqrtx+3))`
`<=>A=(x+4sqrtx+3-7sqrtx-3)/((sqrtx-3)(sqrtx+3))`
`<=>A=(x-3sqrtx)/((sqrtx-3)(sqrtx+3))`
`<=>A=(sqrtx(sqrtx-3))/((sqrtx-3)(sqrtx+3))`
`<=>A=sqrtx/(sqrtx+3)`
\(A=\dfrac{\sqrt{x}+1}{\sqrt{x}-3}-\dfrac{7\sqrt{x}+3}{x-9}\)
\(=\dfrac{\left(\sqrt{x}+1\right)\left(\sqrt{x}+3\right)}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}-\dfrac{7\sqrt{x}+3}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\)
\(=\dfrac{x+3\sqrt{x}+\sqrt{x}+3}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}-\dfrac{7\sqrt{x}+3}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\)
\(=\dfrac{x+4\sqrt{x}+3-7\sqrt{x}+3}{\text{}\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\)
\(=\dfrac{x-3\sqrt{x}+7}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\)
\(=\dfrac{\sqrt{x}\left(\sqrt{x}-3\right)+7}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\)
\(=\dfrac{\sqrt{x}+7}{\sqrt{x}+3}\)
