Đáp án + Giải thích các bước giải:
$\text{1)}$
$\text{Ta có:}$
$\text{5x(x - 3) - x + 3 = 0}$
$\text{⇔ 5x(x - 3) - (x - 3) = 0}$
$\text{⇔ (5x - 1)(x - 3) = 0}$
$\text{⇔ $\left[\begin{matrix} 5x-1=0\\ x-3=0\end{matrix}\right.$}$
$\text{+, 5x - 1 = 0}$
$\text{⇔ x = $\dfrac{1}{5}$ }$
$\text{+, x - 3 = 0}$
$\text{⇔ x = 3}$
$\text{Vậy x = 3 hoặc x = $\dfrac{1}{5}$}$
$\text{2)}$
$\text{$x^{2}$ + 4x - $y^{2}$ + 4 = ($x^{2}$ + 4x + 4) - $y^{2}$ }$
$\text{= $(x + 2)^{2}$ - $y^{2}$ }$
$\text{= (x + 2 - y)(x + 2 + y)}$
