-4x2 -18x -20 = 0
ax2 bx c = 0
a = -4
b = -18
c = -20
Δ = b2-4ac
Δ = -18² - (4 * -4 * -20)
Δ = 324 - (4*80)
Δ = 324 - (320)
Δ = 4 Δ > 0
-4x2-18x-20=0
x = -b ∓ √Δ 2a
x' = 18 - √4 2*-4 = 18 - 2.0 -8 = 16.0 -8 = -2.0
x" = 18 + √4 2*-4 = 18 + 2.0 -8 = 20.0 -8 = -2.5
x' = -32.0
x" = -40.0
S = {x ∈ R / x' = -32.0, x" = -40.0 }