$(2x -18).(3x +12) = 0$
$⇒ 6x² +24x -54x -216 = 0$
$⇒ 6x² -30x -216 = 0$
$⇒ 6x.(x -9) +24.(x -9) = 0$
$⇒ (x -9).(6x +24) = 0$
$⇒ \left[ \begin{array}{l}x -9=0\\6x +24=0\end{array} \right. ⇒ \left[ \begin{array}{l}x=9\\x=-4\end{array} \right.$
$Vậy$ `x ∈ {9; -4}`