a.

C1 :
Ta có :

`2023/2024 < 1` và `2024/2023 > 1`

`=> 2023/2024 < 2024/2023`

`=> - 2023/2024 > -2024/2023` (đpcm)

C2 :

`-2023/2024 = - ( 2023 . 2023 ) / (2024 . 2023) = - 2023^2 / (2023 . 2024)`

`-2024 / 2023 = - ( 2024 . 2024 ) / (2023 . 2024) = - 2024^2/ (2023 . 2024)`

Vì `2023^2 < 2024^2`

nên `-2023^2 > -2024^2`

`=>  - 2023/2024 > -2024/2023` (đpcm)

b.

C1 :

Ta có :

`34/11 = 306/99`

`26/9 = 286/99`

Vì `306 > 286` nên `306/99 > 286/99`

`=> 34/11 > 26/9` ( đpcm )

C2 :

`34/11 - 26/9`

`= ((34 . 9) - (26 . 11))/(9.11)`

`= (306 - 286)/99`

`= 20/99 > 0`

`=> 34/11 > 26/9` ( đpcm )

C3 :

`34/11 = 3 + 1/11`

`26/9 = 2 + 8/9`

Ta có :

`3 + 1/11 > 3`

`2 + 8/9 < 3`

`=> 34/11 > 26/9` ( đpcm )