Đáp án + Giải thích các bước giải:
`(x-1)/(2019)+(x-2)/(2018)=(x-3)/(2017)+(x-4)/(2016)`
`->((x-1)/(2019)-1)+((x-2)/(2018)-1)=((x-3)/(2017)-1)+((x-4)/(2016)-1)`
`->((x-1)/(2019)-(2019)/(2019))+((x-2)/(2018)-(2018)/(2018))=((x-3)/(2017)-(2017)/(2017))+((x-4)/(2016)-(2016)/(2016))`
`->(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=0` . Vì `(1)/(2019)+(1)/(2018)-(1)/(2017)-(1)/(2016)\ne0`
`->x=2020`
