$#DAnh$

4.

Đkxđ : `x>=0`

`(3sqrtx - 5)/2 - (2sqrtx - 7)/3 = sqrtx - 1`

`(3(3sqrtx - 5))/6 - (2(2sqrtx - 7))/6 = (6(sqrtx - 1))/6`

`9sqrtx - 15 - 4sqrtx + 14 = 6sqrtx - 6`

`9sqrtx - 15 - 4sqrtx + 14 - 6sqrtx + 6 = 0`

`-sqrtx + 5 = 0`

`sqrtx = 5`

`x = 25` `(tm)`

Vậy `S={25}` .