Đáp án:
$S=\{\dfrac{-1}{2};-2\}$
Giải thích các bước giải:
$2x^2 + 5x + 2 = 0$
$→2x^2+5x=-2$
$→x^2+\dfrac{5}{2}x=-1$
$→x^2+2x\dfrac{5}{4}+(\dfrac{5}{4})^2=-1+(\dfrac{5}{4})^2$
$→(x+\dfrac{5}{4})^2=\dfrac{9}{16}$
$→\left[ \begin{array}{l}x+\dfrac{5}{4}=\dfrac{3}{4}\\x+\dfrac{5}{4}=-\dfrac{3}{4}\end{array} \right.$
$→\left[ \begin{array}{l}x=\dfrac{-1}{2}\\x=-2\end{array} \right.$
$Vậy...$
