`|x+13/7|+|x+2020/2021|+|x-1|=0`
Vì : `|x+13/7|;|x+2020/2021|;|x-1|≥0`
`⇒|x+13/7|+|x+2020/2021|+|x-1|≥0`
$⇒\begin{cases}|x+\dfrac{13}{7}|=0⇒x+\dfrac{13}{7}=0⇒x=\dfrac{-13}{7}\\|x+\dfrac{2020}{2021}|=0⇒x+\dfrac{2020}{2021}=0⇒x=\dfrac{-2020}{2021}\\|x-1|=0⇒x-1=0⇒x=1\end{cases}$
Vì `x` không thể đồng thời bằng `\frac{-13}{7};\frac{-2020}{2021}` và `1`
$⇒x∈\varnothing$
