Đáp án: $A\ge \dfrac{6061}{2}$
Giải thích các bước giải:
Ta có:
$A=|x+2020|+|2x-2021|$
$\to A=|x+2020|+2|x-\dfrac{2021}{2}|$
$\to A=|x+2020|+|x-\dfrac{2021}{2}|+|x-\dfrac{2021}{2}|$
$\to A=|x+2020|+|\dfrac{2021}{2}-x|+|x-\dfrac{2021}{2}|$
$\to A\ge |x+2020+\dfrac{2021}{2}-x|+0$
$\to A\ge \dfrac{6061}{2}$
Dấu = xảy ra khi $\begin{cases} (x+2020)(\dfrac{2021}{2}-x)\ge 0\\ x-\dfrac{2021}{2}=0\end{cases}$
$\to x=\dfrac{2021}{2}$