Đáp án: $x=2020$.
Giải thích các bước giải:
`{x-1}/2019 + {x-2}/2018 = {x-3}/2017 + {x-4}/2016`
`⇔ {x-1}/2019 + {x-2}/2018 -2= {x-3}/2017 + {x-4}/2016 -2`
`⇔ ({x-1}/2019 -1) + ({x-2}/2018 -1)= ({x-3}/2017 -1) + ({x-4}/2016 -1)`
`⇔ {x-2020}/2019 + {x-2020}/2018 = {x-2020}/2017 + {x-2020}/2016`
`⇔ {x-2020}/2019 + {x-2020}/2018 - {x-2020}/2017 - {x-2020}/2016 =0`
`⇔ (x-2020).(1/2019 + 1/2018 - 1/2017 - 1/2016)=0`
`⇔ x=2020` (`1/2019 + 1/2018 - 1/2017 - 1/2016 \ne 0`)
Vậy `x=2020`.