-6x2-12x-6=0

Δ = b2-4ac

Δ = -12² - (4 * -6 * -6)

Δ = 144 - (4*36)

Δ = 144 - (144)

Δ = 0      Δ = 0

x = -b 2*a

x = 12 2*-6

x = -1.0

S = {x ∈ R / x = -1.0}