`33) 16x^2 - 25 = (4x - 5)(2x + 1)`

`<=> 16x^2 - 25 = 8x^2 - 6x - 5`

`<=> 8x^2 + 6x - 20 = 0`

`<=> 8x^2 + 16x - 10x - 20 = 0`

`<=> 8x(x + 2) - 10(x + 2)=  0`

`<=> (x + 2)(8x - 10) = 0`

`<=> x +2  = 0` hoặc `8x - 10 = 0`

`<=> x = -2` hoặc `x = 5/4`

Vậy `S = {-2; 5/4}`

`-------------`

`35) (9x^2 - 4)(x + 1) = (3x + 2)(x^2 - 1)`

`<=> 9x^3 - 4x + 9x^2 - 4 = 3x^3 + 2x^2 - 3x - 2`

`<=> 6x^3 + 7x^2 - x - 2 = 0`

`<=> 6x^3 + 6x^2 + x^2 + x - 2x - 2= 0 `

`<=> 6x^2(x + 1) + x(x + 1) - 2(x + 1) = 0`

`<=> (x + 1)(6x^2 + x - 2)= 0 `

`<=> (x + 1)(3x + 2)(2x - 1) = 0`

`<=> x + 1 = 0` hoặc `3x + 2 =0` hoặc `2x - 1 = 0`

`<=> x =-1` hoặc `x = -2/3` hoặc `x = 1/2`

Vậy `S = {-1; -2/3; 1/2}`