`(2019a-2020)^2017=(2019a-2020)^2018`
`⇒(2019a-2020)^2018-(2019a-2020)^2017=0`
`⇒(2019a-2020)^2017[(2019a-2020)-1]=0`
`⇒(2019a-2020)^2017(2019a-2021)=0`
\(\left[ \begin{array}{l}(2019a-2020)^{2017}=0\\2019a-2021=0\end{array} \right.\)
\(⇒\left[ \begin{array}{l}2019a-2020=0\\a=\dfrac{2021}{2019}\end{array} \right.\)
\(⇒\left[ \begin{array}{l}a=\dfrac{2020}{2019}\\a=\dfrac{2021}{2019}\end{array} \right.\)
Vậy `x∈{2020/2019;2021/2019}`