`x^2-4x+5=0`
`⇔x^2+x-5x+5=0`
`⇔x(x+1)-5(x+1)=0`
`⇔(x+1)(x-5)=0`
`⇔`\(\left[ \begin{array}{l}x+1=0\\x-5=0\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}x=-1\\x=5\end{array} \right.\)
Vậy `S={-1;5}.`
`2x^2-6x+8=0`
`⇔2x^2+2x-8x+8=0`
`⇔2x(x+1)-8(x+1)=0`
`⇔(x+1)(2x-8)=0`
`⇔`\(\left[ \begin{array}{l}x+1=0\\2x-8=0\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}x=-1\\2x=8\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}x=-1\\x=4\end{array} \right.\)
Vậy `S={-1;4}.`
