`\sqrt{9-12x+4x^2}=4`
`⇒\sqrt{3^2-2.3.2x.(2x)^2}=4`
`⇒\sqrt{(3-2x)^2}=4`
`⇒|3-2x|=4`
`⇒`\(\left[ \begin{array}{l}3-2x=4\\3-2x=-4\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}-2x=4-3\\-2x=-4-3\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}-2x=-1\\-2x=-7\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}x=\dfrac{1}{2}\\x=\dfrac{7}{2}\end{array} \right.\)
`\text{Vậy}` ` S={1/2;7/2.}`
