20x2 -8x -1 = 0
ax2 bx c = 0
a = 20
b = -8
c = -1
Δ = b2-4ac
Δ = -8² - (4 * 20 * -1)
Δ = 64 - (4*-20)
Δ = 64 - (-80)
Δ = 144 Δ > 0
20x2-8x-1=0
x = -b ∓ √Δ 2a
x' = 8 - √144 2*20 = 8 - 12.0 40 = -4.0 40 = -0.1
x" = 8 + √144 2*20 = 8 + 12.0 40 = 20.0 40 = 0.5
x' = -40.0
x" = 200.0
S = {x ∈ R / x' = -40.0, x" = 200.0 }