4x2 - 1 = (2x + 1).(3x - 5)
<=> (2x)2 - 12 = (2x + 1).(3x - 5)
<=> (2x - 1).(2x + 1) = (2x + 1).(3x - 5)
<=> (2x - 1).(2x + 1) - (2x + 1).(3x - 5) = 0
<=> (2x + 1).(2x - 1 - 3x + 5) = 0
<=> (2x - 1).(4 - x) = 0
<=> 2x - 1 = 0 hoặc 4 - x = 0
<=> x = 1/2 hoặc x = 4
Vậy S = {1/2; 4}.