Hướng dẫn trả lời:
$\text{a) 2x.(x - 2) + 3x = 6.}$
$\text{⇒ 2x.(x - 2) + 3x - 6 = 0.}$
$\text{⇒ 2x.(x - 2) + 3.(x - 2) = 0.}$
$\text{⇒ (x - 2).(2x + 3) = 0.}$
$\text{⇒ \(\left[ \begin{array}{l}x-2=0.\\2x+3=0.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}x=2.\\2x=3.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}x=2.\\x=-\dfrac{3}{2}.\end{array} \right.\)}$
$\text{Vậy x = 2 hoặc x = $-\dfrac{3}{2}$.}$
$\text{b) $(2x - 3)^2$ - $81x^2$ = 0.}$
$\text{⇒ $(2x - 3)^2$ - $(9x)^2$ = 0.}$
$\text{⇒ [(2x - 3) + 9x].[(2x - 3) - 9x] = 0.}$
$\text{⇒ (2x - 3 + 9x).(2x - 3 - 9x) = 0.}$
$\text{⇒ (11x - 3).(-7x - 3) = 0.}$
$\text{⇒ \(\left[ \begin{array}{l}11x-3=0.\\-7x-3=0.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}11x=3.\\-7x=3.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}x=\dfrac{3}{11}.\\x=-\dfrac{3}{7}.\end{array} \right.\)}$
$\text{Vậy x = $\dfrac{3}{11}$ hoặc x = $-\dfrac{3}{7}$.}$
