4x2 - 1 = (2x + 1)(3x - 5)
<=> 6x2 - 10x + 3x - 5 - 4x2 + 1 = 0
<=> 2x2 - 7x - 4 = 0
<=> 2x2 - 8x + x - 4 = 0
<=> 2x(x - 4) + (x - 4) = 0
<=> (x - 4)(2x + 1) = 0
<=> \(\left[{}\begin{matrix}2x+1=0\\x-4=0\end{matrix}\right.\)
<=> \(\left[{}\begin{matrix}x=-\dfrac{1}{2}\\x=4\end{matrix}\right.\)
Vậy S = {- 0,5 : 4}
