Đáp án+Giải thích các bước giải:
`A=\frac{x}{x-4}+\frac{1}{\sqrt{x}-2}+\frac{1}{\sqrt{x}+2}(x>=0,x\ne4)`
`=\frac{x}{(\sqrt{x}-2)(\sqrt{x}+2)}+\frac{\sqrt{x}+2}{(\sqrt{x}-2)(\sqrt{x}+2)}+\frac{\sqrt{x}-2}{(\sqrt{x}-2)(\sqrt{x}+2)}`
`=\frac{x+\sqrt{x}+2+\sqrt{x}-2}{(\sqrt{x}-2)(\sqrt{x}+2)}`
`=\frac{x+2\sqrt{x}}{(\sqrt{x}-2)(\sqrt{x}+2)}`
`=\frac{\sqrt{x}(\sqrt{x}+2)}{(\sqrt{x}-2)(\sqrt{x}+2)}`
`=\frac{\sqrt{x}}{\sqrt{x}-2}`
`b)x=36`
`=>A=\frac{\sqrt{36}}{\sqrt{36}+2}=6/(6+2)=6/8=3/4`
`c)A=-1/3`
`=>\frac{\sqrt{x}}{\sqrt{x}-2}=-1/3`
`<=>3\sqrt{x}=-\sqrt{x}+2`
`<=>4\sqrt{x}=2`
`<=>\sqrt{x}=1/2`
`<=>x=1/4(tm)`
Vậy với `x=1/4` thì `A=-1/3`
