(3x + 2)(x2 - 1) = (9x2 - 4)(x + 1)
<=> (3x + 2)(x - 1)(x + 1) - (3x + 2)(3x - 2)(x + 1) = 0
<=> (3x + 2)(x + 1)(x - 1 - 3x + 2) = 0
<=> (3x + 2)(x + 1)(-2x + 1) = 0
<=> \(\left[{}\begin{matrix}3x+2=0\\x+1=0\\1-2x=0\end{matrix}\right.\)
<=> \(\left[{}\begin{matrix}x=-\frac{2}{3}\\x=-1\\x=\frac{1}{2}\end{matrix}\right.\)
Vậy S = {-2/3; 1/2; -1}