`(x-2)^3 + (3x-1)(3x +1) = (x+1)^3`
`<=> x^3 - 6x^2 + 12x - 8 + 9x^2 - 1 = (x+1)^3`
`<=> x^3 - 6x^2 + 12x - 8 + 9x^2 - 1 = x^3 + 3x^2 + 3x + 1`
`<=> x^3 - 6x^2 + 12x - 8 + 9x^2 - 1 - x^3 - 3x^2 - 3x - 1 = 0`
`<=> 9x - 10 = 0`
`<=> 9x = 10`
`<=> x = 10/9`
Vậy `S={10/9}`
$\boxed{\text{Nhyy}}$