Giải thích các bước giải:

$a) (2x + 1)(3x - 1) = 0$

$\Leftrightarrow \left[\begin{aligned} 2x + 1 &= 0 \\ 3x - 1 &= 0 \end{aligned}\right.$

$\Leftrightarrow \left[\begin{aligned} x &= -\dfrac{1}{2} \\ x &= \dfrac{1}{3} \end{aligned}\right.$

$b) (3x + 1)(2 - 3x) = 0$

$\Leftrightarrow \left[\begin{aligned} 3x + 1 &= 0 \\ 2 - 3x &= 0 \end{aligned}\right.$

$\Leftrightarrow \left[\begin{aligned} 3x &= -1 \\ 3x &= 2 \end{aligned}\right.$

$\Leftrightarrow \left[\begin{aligned} x &= -\dfrac{1}{3} \\ x &= \dfrac{2}{3} \end{aligned}\right.$

$c) (x + 5)(3x - 9) = 0$

$\Leftrightarrow \left[\begin{aligned} x + 5 &= 0 \\ 3x - 9 &= 0 \end{aligned}\right.$

$\Leftrightarrow  \left[\begin{aligned} x &= -5 \\ x &= 3 \end{aligned}\right.$

$d) 3x .(x + 7) = 0$

$\Leftrightarrow \left[\begin{aligned} 3x &= 0 \\ x + 7 &= 0 \end{aligned}\right.$

$\Leftrightarrow \left[\begin{aligned} x &= 0 \\ x &= -7 \end{aligned}\right.$