-4x2 -8x -4 = 0

ax2 bx c = 0

a = -4

b = -8

c = -4

Δ = b2-4ac

Δ = -8² - (4 * -4 * -4)

Δ = 64 - (4*16)

Δ = 64 - (64)

Δ = 0      Δ = 0

x = -b 2*a

x = 8 2*-4

x = -1.0

S = {x ∈ R / x = -1.0}