`a)(2x+4)(3-x)=0`
`⇔` \(\left[ \begin{array}{l}2x+4=0\\3-x=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}2x=-4\\x=3\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=-2\\x=3\end{array} \right.\)
Vậy `S={-2;3}`
`b)3x^2+9x=0`
`⇔3x(x+3)=0`
`⇔` \(\left[ \begin{array}{l}3x=0\\x+3=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=0\\x=-3\end{array} \right.\)
Vậy `S={0;-3}`
`c)x^2-4=(x-2)(2x+6)`
`⇔(x-2)(x+2)-(x-2)(2x+6)=0`
`⇔(x-2)(x+2-2x-6)=0`
`⇔(x-2)(-x-4)=0`
`⇔` \(\left[ \begin{array}{l}x-2=0\\-x-4=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=2\\x=-4\end{array} \right.\)
Vậy `S={2;-4}`
`d)x^2-13x-48=0`
`⇔x^2-16x+3x-48=0`
`⇔x(x-16)+3(x-16)=0`
`⇔(x-16)(x+3)=0`
`⇔` \(\left[ \begin{array}{l}x-16=0\\x+3=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=16\\x=-3\end{array} \right.\)
Vậy `S={16;-3}`
