Đáp án+Giải thích các bước giải:
`f) (x+3)/2020 + (4x+8)/2019 - (5x+5)/2018 = 0`
`<=> (x+3)/2020 + (4x+8)/2019 + (-5x -5)/2018 = 0`
`<=> (x+3)/2020 - 1 + (4x+8)/2019 - 4 + (-5x-5)/2018 + 5 = 0`
`<=> (x+3 - 2020)/2020 + (4x + 8 - 2019.4)/2019 + (-5x - 5 + 2018 . 5)/2018 = 0`
`<=> (x-2017)/2020 + (4x -8068)/2019 + (-5x + 10085)/2018 = 0`
`<=> (x-2017)/2020 + 4. ( x - 2017)/2019 + (-5 . (x-2017))/2018 = 0`
`<=> (x-2017)(1/(2020)+4/(2019)-5/(2018))=0`
`<=> x - 2017 =0 ( vì 1/(2020)+4/(2019)-5/(2018)\ne0)`
`<=> x = 2017`
Vậy `S={2017}`
