Explicação passo-a-passo:

x . x - 5 . x = - 6

x² - 5x + 6=0

∆= (-5)² - 4.1.6

∆= 25 - 24

∆= 1

x = - (-5) ±√1/2.1

x = 5 ±1/2

x1= 5+1/2= 6/2= 3

x2= 5-1/2= 4/2= 2

S = { 2 ,3}