$\\$
`x/2021 + (x+1)/2020 + ... + (x+2020)/1 + 2021=0`
`-> x/2021 + (x+1)/2020 + ... + (x+2020)/1 + \underbrace{1+1+...+1+1}_{ \text{2021 chữ số 1}} =0`
`-> (x/2021 + 1) + ( (x+1)/2020 + 1) + ... + ( (x+2020)/1 + 1) =0`
`-> (x/2021 + 2021/2021) + ( (x+1)/2020 + 2020/2020) + ... + ( (x+2020)/1 + 1/1)=0`
`-> (x+2021)/2021 + (x+1+2020)/2020 + ... + (x+2020 + 1)/1=0`
`-> (x+2021)/2021 + (x + 2021)/2020 + ... + (x+2021)/1 =0`
`-> (x+2021) (1 + ... + 1/2020 + 1/2021)=0`
`-> x+2021 =0` (Do `1+...+1/2020 + 1/2021 \ne 0`)
`->x=0-2021`
`->x=-2021`
Vậy `x=-2021`
