Verified answer

Vamos là.

x*(x - 2) = 2*(x + 6)

tudo de um lado

x*(x - 2) - 2*(x + 6) = 0

multiplique

x² - 2x - 2x - 12 = 0

simplifique

x² - 4x - 12 = 0

os coeficientes

a = 1, b =-4, c = -12

delta

d² = 16 + 48 = 64

d = 8

as raizes

x1 = (4 + 8)/2 = 12/2 = 6

x2 = (4 - 8)/2 = -4/2 = -2

S = (-2, 6)