`[2-\sqrt{x}]/x=3` `ĐK: x > 0`
`<=>[2-\sqrt{x}]/x=[3x]/x`
`=>2-\sqrt{x}=3x`
`<=>3x+\sqrt{x}-2=0`
`<=>3x+3\sqrt{x}-2\sqrt{x}-2=0`
`<=>3\sqrt{x}(\sqrt{x}+1)-2(\sqrt{x}+1)=0`
`<=>(\sqrt{x}+1)(3\sqrt{x}-2)=0` mà `\sqrt{x}+1 > 0`
`=>3\sqrt{x}-2=0`
`<=>\sqrt{x}=2/3<=>x=4/9` (t/m)
Vậy `S={4/9}`