Đáp án:
$\text{ 2x² + 5x + 2 =0 }$
$\text{⇔ 2x² + x + 4x + 2 =0 }$
$\text{⇔ x(2x +1)+2(2x+1) =0 }$
$\text{⇔(2x+1)(x+2)=0 }$
$\text{⇔ \(\left[ \begin{array}{l}2x+1=0\\x+2=0\end{array} \right.\) }$
$\text{⇔\(\left[ \begin{array}{l}x=-\dfrac{1}{2}\\x=-2\end{array} \right.\) }$
$\text{Vậy x ∈ { -$\dfrac{1}{2}$ ; -2} }$