ta có : \(\left(2x-1\right)\left(x+2\right)=0\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{1}{2}\\x=-2\end{matrix}\right.\)
mà ta có : \(\left(2x-1\right)\left(x+2\right)=2x^2+3x-2\) \(\Rightarrow a=2>0\)
\(\Rightarrow\left(2x-1\right)\left(x+2\right)\le0\Leftrightarrow-2\le x\le\dfrac{1}{2}\)