Đáp án:
`\sqrt{x^2 - 5} = 2` `ĐKXĐ: x≥ \sqrt{5} , x≤ -\sqrt{5}`
`<=> \sqrt{(x^2 - 5)^2} = 2^2`
`<=> x^2 - 5= 4`
`<=> x^2 = 9`
`<=> x= ±3`
Vậy `S={±3}`
`\sqrt{x^2 - 10x + 25} = 7`
`<=> \sqrt{(x - 5)^2}` = `7`
`<=> | x - 5| = 7`
`<=>` \(\left[ \begin{array}{l}x-5=7\\x-5=-7\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=12\\x=-2\end{array} \right.\)
Vậy `S={-2 ; 12}`
