Đáp án:
`C>D`
Giải thích các bước giải:
`C=(2019^2019+1)/(2019^2020+1`
`=>2019C=(2019.(2019^2019+1))/(2019^2020+1)`
`=>2019C=(2019^2020+2019)/(2019^2020+1`
`=>2019C=(2019^2020+1+2018)/(2019^2020+1`
`=>2019C=(2019^2020+1)/(2019^2020+1)+2018/(2019^2020+1`
`=>2019C=1+2018/(2019^2020+1`
`D=(2019^2020-2)/(2019^2021-2`
`=>2019D=(2019.(2019^2020-2))/(2019^2021-2)`
`=>2019D=(2019^2021-4038)/(2019^2021-2)`
`=>2019D=(2019^2021-2-4036)/(2019^2021-2`
`=>2019D=(2019^2021-2)/(2019^2021-2)+(-4036)/(2019^2021-2)`
`=>2019D=1+(-4036)/(2019^2021-2`
`=>2018/(2019^2021+1)>(-4036)/(2019^2021-2)`
`=>1+2018/(2019^2021-1)>1+(-4036)/(2019^2021-2`
`=>2019C>2019D`
`=>C>D`
Vậy `C>D`.
