$(x-3)(2x-1)=(2x-1)(2x+3)$
⇔ $(x-3)(2x-1)-(2x-1)(2x+3)=0$
⇔ $(2x-1)(x-3-2x-3)=0$
⇔ $(2x-1)(-x-6)=0$
⇔ \(\left[ \begin{array}{l}2x-1=0\\-x-6=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=\frac{1}{2} \\x=-6\end{array} \right.\)
Vậy $S=${$\frac{1}{2};-6 $}