-x2-2x-1=0

Δ = b2-4ac

Δ = -2² - (4 * -1 * -1)

Δ = 4 - (4*1)

Δ = 4 - (4)

Δ = 0      Δ = 0

x = -b 2*a

x = 2 2*-1

x = -1.0

S = {x ∈ R / x = -1.0}