`(x-4)/2021 + (x-3)/2022 = (x-2)/2023 + (x-1)/2024`

`⇔(x-4)/2021 - 1 + (x-3)/2022 -1 = (x-2)/2023 -1 + (x-1)/2024 - 1`

`⇔(x-4)/2021 - 2021/2021 + (x-3)/2022 - 2022/2022 = (x-2)/2023 - 2023/2323 + (x-1)/2024 - 2024/2024`

`⇔(x-4-2021)/2021 + (x-3-2022)/2022 = (x-2-2023)/2023 + (x-1-2024)/2024`

`⇔(x-2025)/2021 + (x-2025)/2022 - (x-2025)/2023 - (x-2025)/2024= 0`

`⇔(x-2025).(1/2021+1/2022-1/2023-1/2024)=0`

Vì: `1/2021+1/2022-1/2023-1/2024 ne 0`

`=> x-2025=0`

`=>x=2025`