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}