Tìm x (x-1)/2020 + (x-2)/2019=(x-3)/2018 + (x-4)/2017

Đáp án:

` (x-1)/2020 + (x-2)/2019 = (x-3)/2018 + (x-4)/2017`

` => ((x-1)/2020 – 1) + ((x-2)/2019-1) = ((x-3)/2018-1) + ((x-4)/2017-1)`

` => (x-2021)/2020 + (x-2021)/2019 = (x-2021)/2018 + (x-2021)/2017`

` => (x-2021) * (1/2020 + 1/2019 – 1/2018 – 1/2017) = 0`

Ta thấy phần trong ngoặc lớn luôn khác `0`

` => (x-2021) * (1/2020 + 1/2019 – 1/2018 – 1/2017) = 0` khi 

` x – 2021 = 0`

` \to x = 2021`

Vậy ` x= 2021`