`(3x-1)^2-9=0`
`<=>(3x-1)^2-3^2=0`
`<=>(3x-1-3)(3x-1+3)=0`
`<=>(3x-4)(3x+2)=0`
`<=>` \(\left[ \begin{array}{l}3x-4=0\\3x+2=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}3x=4\\3x=-2\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=\frac{4}{3}\\x=\frac{-2}{3}\end{array} \right.\)
vậy `S={4/3;-2/3}`