Đáp án: `2018 < x < 2019`
Giải thích các bước giải:
`(2020 - x)/(2019 - x) > 2`
`<=> (2020 - x)/(2019 - x) - 2 >0`
`<=> (2020 - x - 2(2019 - x))/(2019 - x) > 0`
`<=> (2020 - x - 4038 + 2x)/(2019 - x) > 0`
`<=> (x - 2018)/(2019 - x) > 0`
Xét `2TH:`
`TH1:`
\(\left\{ \begin{array}{l}x - 2018 > 0\\2019 - x > 0\end{array} \right.\)
`<=>` \(\left\{ \begin{array}{l}x > 2018\\x < 2019\end{array} \right.\)
`=> 2018 < x < 2019`
`TH2:`
\(\left\{ \begin{array}{l}x - 2018 < 0\\2019 - x < 0\end{array} \right.\)
`<=>` \(\left\{ \begin{array}{l}x < 2018\\x > 2019\end{array} \right.\)
`=> loại`
