${a)}$ ${6 . x + 3 . x + 4 . x = 105}$
${⇒x.(6+3+4)=105}$
${⇒x.13=105}$
${⇒x=105:13}$
⇒ ${x}$=$\frac{105}{13}$
$\text{Vậy x = $\frac{105}{13}$ }$
${b)}$ ${(3.x-18).(8-2.x) = 0}$
⇒ \(\left[ \begin{array}{l}3.x-18=0\\8-2.x=0\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}3.x=0+18\\2.x=8-0\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}3.x=18\\2.x=8\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=18:3\\x=8:2\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=6\\x=4\end{array} \right.\)
$\text{Vậy \(\left[ \begin{array}{l}x=6\\x=4\end{array} \right.\) }$
$\text{CHÚC BẠN HỌC TỐT!!}$
