20x2 -8x -9 = 0
ax2 bx c = 0
a = 20
b = -8
c = -9
Δ = b2-4ac
Δ = -8² - (4 * 20 * -9)
Δ = 64 - (4*-180)
Δ = 64 - (-720)
Δ = 784 Δ > 0
20x2-8x-9=0
x = -b ∓ √Δ 2a
x' = 8 - √784 2*20 = 8 - 28.0 40 = -20.0 40 = -0.5
x" = 8 + √784 2*20 = 8 + 28.0 40 = 36.0 40 = 0.9
x' = -200.0
x" = 360.0
S = {x ∈ R / x' = -200.0, x" = 360.0 }