`x-\sqrt{x}-2=0` `ĐK: x >= 0`
`<=>(\sqrt{x})^2-2\sqrt{x}+\sqrt{x}-2=0`
`<=>\sqrt{x}(\sqrt{x}-2)+(\sqrt{x}-2)=0`
`<=>(\sqrt{x}-2)(\sqrt{x}+1)=0`
`<=>` $\left[\begin{matrix} \sqrt{x}=2\\ \sqrt{x}=-1\text{ (Vô lí)}\end{matrix}\right.$
`<=>x=4` (t/m)
Vậy `S={4}`
\(x-\sqrt{x}-2=0\left(đkxđ:x\ge0\right)\\ \Leftrightarrow x+\sqrt{x}-2\sqrt{x}-2=0\\ \Leftrightarrow\sqrt{x}\left(\sqrt{x}+1\right)-2\left(\sqrt{x}+1\right)=0\\ \Leftrightarrow\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}\sqrt{x}-2=0\\\sqrt{x}+1=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=2\\\sqrt{x}=-1\left(Loại\right)\end{matrix}\right.\\ \Leftrightarrow x=4\)