`2x^2 - 11x + 13 = 3sqrt(9x - 4)((11 - sqrt17)/4 >= x >= 4/9 ; x >= (11 + sqrt17)/4)`

`<=> (2x^2 - 11x + 13)^2 = (3sqrt(9x - 4))^2`

`<=> 4x^4 - 44x^3 + 173x^2 - 286x + 169 = 81x - 36`

`<=> 4x^4 - 44x^3 + 173x^2 - 367x + 205 = 0`

`<=> (x^2 - 7x + 5)(4x^2 - 16x + 41) = 0`

`+) x^2 - 7x = 5 = 0 <=> x = (7 +- sqrt29)/2 (tm)`

`+) 4x^2 - 16x + 41 = 0 <=>` pt vô nghiệm

Vậy : `S = {(7 +- sqrt29)/2}`