a)
$\sqrt{x - 1}$ `- 3 = 2` (đk : x ≥ 1)
⇒ $\sqrt{x - 1}$ = 5
`⇒ x - 1 = 25`
`⇒ x = 26 (tm)`
`Vậy x = 26`
b)
5$\sqrt{x^2 - 10x + 25}$ `- 12 = 3`
⇔ 5$\sqrt{x^2 - 10x + 25}$ `= 15`
⇒ $\sqrt{x^2 - 10x + 25}$ `= 3`
⇔ $\sqrt{(x - 5)^2}$ `= 3`
`⇒ |x - 5| = 3`
`⇒` \(\left[ \begin{array}{l}x - 5 = 3\\x - 5 = -3\end{array} \right.\)
`⇒` \(\left[ \begin{array}{l}x = 8\\x = 2\end{array} \right.\)
`Vậy S = {8 ; 2}`
