x2 x =0

5x2 -20x +20 = 0

ax2 bx c = 0

a = 5

b = -20

c = 20

Δ = b2-4ac

Δ = -20² - (4 * 5 * 20)

Δ = 400 - (4*100)

Δ = 400 - (400)

Δ = 0      Δ = 0

x = -b 2*a

x = 20 2*5

x = 2.0

S = {x ∈ R / x = 2.0}