Hướng dẫn trả lời:
$\text{a) 5x.(x - 1) = x - 1.}$
$\text{⇒ 5x.(x - 1) - (x - 1) = 0.}$
$\text{⇒ (x - 1).(5x - 1) = 0.}$
$\text{⇒ \(\left[ \begin{array}{l}x-1=0.\\5x-1=0.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}x=1.\\5x=1.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}x=1.\\x=\dfrac{1}{5}.\end{array} \right.\)}$
$\text{Vậy x = 1 hoặc x = $\dfrac{1}{5}$.}$
$\text{b) 2.(x + 5) - $x^2$ - 5x = 0.}$
$\text{⇒ 2.(x + 5) - x.(x + 5) = 0.}$
$\text{⇒ (x + 5).(2 - x) = 0.}$
$\text{⇒ \(\left[ \begin{array}{l}x+5=0.\\2-x=0.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}x= - 5.\\x=2.\end{array} \right.\)}$
$\text{Vậy x = -5 hoặc x = 2.}$
$\text{c) $2x^{2}$ + 5x - 3 = 0.}$
$\text{⇒ $2x^{2}$ + 6x - x - 3 = 0.}$
$\text{⇒ ($2x^{2}$ + 6x) - (x + 3) = 0.}$
$\text{⇒ 2x.(x + 3) - (x + 3) = 0.}$
$\text{⇒ (x + 3).(2x - 1) = 0.}$
$\text{⇒ \(\left[ \begin{array}{l}x+3=0.\\2x-1=0.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}x=-3.\\2x=1.\end{array} \right.\)}$
$\text{⇒ \(\left[ \begin{array}{l}x=-3.\\x=\dfrac{1}{2}.\end{array} \right.\)}$
$\text{Vậy x = -3 hoặc x = $\dfrac{1}{2}$.}$
