Đáp án:
`Amin=2021<=>-2020<=x<=1.`
Giải thích các bước giải:
`A=|x-1|+|x+2020|`
`=|1-x|+|x+2020|`
Ta có:
$\left\{\begin{matrix}|1-x|\ge1-x\\|x+2020|\ge x+2020\end{matrix}\right.$
`=>|1-x|+|x+2020|>=1-x+x+2020=2021`
`=>A>=2021`
Dấu `=` xảy ra `<=>`$\left\{\begin{matrix}1-x\ge0\\x+2020\ge0\end{matrix}\right.$
`=>`$\left\{\begin{matrix}x\le1\\x\ge-2020\end{matrix}\right.$`=>-2020<=x<=1`
Vậy `Amin=2021<=>-2020<=x<=1.`
