Giải thích các bước giải:
`a)`
`\sqrt{9x^2 - 6x + 1} = 3`
`⇔ \sqrt{(3x - 1)^2} = 3`
`⇒ |3x - 1| = 3`
`⇒` \(\left[ \begin{array}{l}3x - 1 = 3\\3x - 1 = -3\end{array} \right.\)
`⇒` \(\left[ \begin{array}{l}x=4/3\\x=-2/3\end{array} \right.\)
`Vậy S = {4/3 ; -2/3}`
`b)`
`\sqrt{4x - 8} - \sqrt{x - 2} + \sqrt{9x - 18} = 12 (đk : x ≥ 2)`
`⇔ \sqrt{4(x - 2)} - \sqrt{x - 2} + \sqrt{9(x - 2)} = 12`
`⇔ 2\sqrt{x - 2} - \sqrt{x - 2} + 3\sqrt{x - 2} = 12`
`⇔ 4\sqrt{x - 2} = 12`
`⇔ \sqrt{x - 2} = 3`
`⇒ x - 2 = 9`
`⇒ x = 11 (tm)`
`Vậy S = {11}`
