`x-2\sqrt{x-1}=4` (ĐKXĐ: `x>=4`)
`<=> x-1-2\sqrt{x-1}+1=4`
`<=> (\sqrt{x-1}-1)^2=4`
`<=>`\(\left[ \begin{array}{l}\sqrt{x-1}-1=2\\\sqrt{x-1}-1=-2\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}\sqrt{x-1}=3\\\sqrt{x-1}=-1 (l)\end{array} \right.\)
`=> x-1=9`
`<=> x=10 (tm)`
Vậy pt có tập nghiệm `S={10}`