Bài giải:

2(x + 3) – x(x + 3)  = 0                                                

$\Leftrightarrow \left( \text{x }+\text{ 3} \right)\left( \text{2 }-\text{ x} \right)\text{ }=\text{ }0$

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

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

Mà x < 0 nên x = -3

Vậy x = -3.