9x²-32-x(3x+16)=0
⇔9x²-32-3x²-16x=0
⇔6x²-16x-32=0
⇔(6x²-24x)+(8x-32)=0
⇔(x-4)(6x+8)=0
⇔2(x-4)(3x+4)=0
⇔\(\left[ \begin{array}{l}x-4=0\\3x+4=0\end{array} \right.\)⇔\(\left[ \begin{array}{l}x=4\\x=\frac{-4}{3}\end{array} \right.\)
Vậy S={4; $\frac{-4}{3}$}.