Ta có: (a - 2018)2 ≥ 0; (b + 2019)2 ≥ 0
=> (a - 2018)2 + (b + 2019)2 ≥ 0
Dấu "=" xảy ra <=> \(\left\{{}\begin{matrix}\left(a-2018\right)^2=0\\\left(b+2019\right)^2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=2018\\b=-2019\end{matrix}\right.\)