3x - (2 căn x) - 1 = 0

`3x - 2sqrtx - 1 =0 (x >= 0)`

`<=> 3x - 3sqrtx + sqrtx - 1 =0`

`<=> 3sqrtx (sqrtx - 1) + (sqrtx - 1) =0`

`<=> (sqrtx - 1)(3sqrtx + 1) =0 `

`<=> sqrtx - 1= 0 \text{ hoặc } 3sqrtx + 1 =0`

`<=> sqrtx = 1 \text{ hoặc } 3sqrtx = - 1 (l)`

`<=> x = 1 (TM)`

Vậy `S = {1}`