5x2+10x+5=0

Δ = b2-4ac

Δ = 10² - (4 * 5 * 5)

Δ = 100 - (4*25)

Δ = 100 - (100)

Δ = 0      Δ = 0

x = -b 2*a

x = -10 2*5

x = -1.0

S = {x ∈ R / x = -1.0}