$\text{ $x^{2}$ - 6x + 8 = 0 }$
$\text{ <=> $x^{2}$ -2x - 4x + 8 = 0}$
$\text{ <=> ( $x^{2}$ -2x ) - ( 4x + 8 ) = 0}$
$\text{ <=> x ( x - 2 ) - 4 ( x - 2 ) = 0 }$
$\text{ <=> ( x - 2 ) ( x - 4 ) = 0 }$
$\text{ <=> }$ $\begin{cases} x - 2 = 0\\\ x - 4 = 0\end{cases}$
$\text{ <=> }$ $\begin{cases} x = 2 \\\ x = 4\end{cases}$
$\text{ Vậy x = 2 hoặc x = 4 .}$
