`(x+5)/2020+(x+4)/2021=(x+3)/2022+(x+2)/2023`
`⇔(x+5)/2020+(x+4)/2021+1+1=(x+3)/2022+(x+2)/2023+1+1`
`⇔((x+5)/2020+1)+((x+4)/2021+1)=((x+3)/2022+1)+((x+2)/2023+1)`
`⇔(x+5+2020)/2020+(x+4+2021)/2021=(x+3+2022)/2022+(x+2+2023)/2023`
`⇔(x+2025)/2020+(x+2025)/2021=(x+2025)/2022+(x+2025)/2023`
`⇔(x+2025)/2020+(x+2025)/2021-(x+2025)/2022-(x+2025)/2023=0`
`⇔(x+2025)(1/2020+1/2021-1/2022-1/2023)=0`
`⇔x+2025=0(` vì `1/2020+1/2021-1/2022-1/2023`$\neq$ `0)`
`⇔x=-2025`
Vậy `S={-2025}`