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`2021 + |2021 - x| = x`
`-> |2021 - x| = x - 2021`
`->` \(\left[ \begin{array}{l}x ≤ 2021\\x ≥ 2021\end{array} \right.\)
* `x ≤ 2021`
`-> 2021 - x = x - 2021`
`-> x + x = 2021 + 2021`
`-> 2x = 4042`
`-> x = 4042 : 2`
`-> x = 2021 (TM)`
* `x ≥ 2021`
`-> x - 2021 = x - 2021`
`-> x -x = 2021 - 2021`
`-> 0x = 0`
`-> x = 0 (KTM)`
Vậy `x = 2021`