Đáp án: `+` Giải thích các bước giải:

`x . 5/14 + 9/14 . (44/12 + 44/20 + 44/30 + 44/42 + 44/56) = -5/4`

`=> 5/14x + 9/14 . 44 . (1/12 + 1/20 + 1/30 + 1/42 + 1/56) = -5/4`

`=> 5/14x + 9/14 . 44 . (1/(3 . 4) + 1/(4 . 5) + 1/(5 . 6) + 1/(6 . 7) + 1/(7 . 8)) = -5/4`

`=> 5/14x + 198/7 . (1/3 - 1/4 + 1/4 -1/5 + ... - 1/7 + 1/7 - 1/8) = -5/4`

`=> 5/14x + 198/7 . (1/3 - 1/8)= -5/4`

`=> 5/14x + 198/7 . 5/24 = -5/4`

`=> 5/14x + 165/28 = -5/4`

`=> 5/14x = -5/4  - 165/28`

`=> 5/14x = -50/7`

`=> x = -50/7 : 5/14`

`=> x = -20`

Vậy: `x=-20`