Bài 2 tìm x a, 3/7-1/7 : |2x-1/3|=3/14 b, x+7/2018 + x+6/2019 + x+5/2020 + x+4/2021

Đáp án:

a, `3/7 – 1/7 : |2x – 1/3| = 3/14`

`<=> 1/7 : |2x – 1/3| = 3/7 – 3/14`

`<=> 1/7 : |2x – 1/3| = 3/14`

`<=> |2x – 1/3| = 1/7 : 3/14`

`<=> |2x – 1/3| = 2/3`

<=>  \(\left[ \begin{array}{l}2x – 1/3 = 2/3\\2x – 1/3 = -2/3\end{array} \right.\) 

<=> \(\left[ \begin{array}{l}x= 1/2\\x=-1/6\end{array} \right.\) 

b, Ta có : 

`(x + 7)/2018 + (x + 6)/2019 = (x + 5)/2020 + (x + 4)/2021`

`<=> ((x + 7)/2018 + 1) + ((x + 6)/2019  + 1) = ((x + 5)/2020  + 1) + ((x + 4)/2021 + 1)`

`<=> (x + 2025)/2018 + (x + 2025)/2019 = (x + 2025)/2020 + (x + 2025)/2021`

`<=> (x + 2025)/2018 + (x + 2025)/2019 –  (x + 2025)/2020 –  (x + 2025)/2021 = 0`

`<=> (x + 2025) . (1/2018 + 1/2019 – 1/2020 – 1/2021) = 0`

Do `1/2018 + 1/2019 – 1/2020 – 1/2021 \ne 0`

`<=> x + 2025 = 0`

`<=> x = -2025`

Giải thích các bước giải: