Đáp án:

`3/(x - 5) = -4/(x + 2) (x ne 5 ; x ne -2)`

`3(x + 2) = -4(x - 5)`

`3x + 6 = -4x + 20`

`7x = 14`

`x = 2`

Vậy `x = 2`

`---`

`2 3/4x - 1 4/5x = 1`

`11/4x - 9/5x = 1`

`19/20x = 1`

`x = 20/19`

Vậy `x = 20/19`

`---`

`(x - 7/2) : 3 1/2 - 5/2 = -1 3/4`

`(x - 7/2) : 7/2 - 5/2 = -7/4`

`(x - 7/2) : 7/2 = 3/4`

`x - 7/2 = 3/4 . 7/2`

`x - 7/2 = 21/8`

`x = 21/8 + 7/2`

`x = 49/8`

Vậy `x = 49/8`