`text(Ta có :)`
`2021^2021 - 2021^2020`
`= 2021^2020 . 2021 - 2021^2020 . 1`
`= 2021^2020(2021 - 1)`
`2021^2019 - 2021^2018`
`= 2021^2018 . 2021 - 2021^2018 . 1`
`= 2021^2018(2021 - 1)`
` Vì 2021^2020 > 2021^2018`
`⇒ 2021^2020(2021 - 1) > 2021^2018(2021 - 1)`
`⇒ x > y`