-1x2 -12x -20 = 0
ax2 bx c = 0
a = -1
b = -12
c = -20
Δ = b2-4ac
Δ = -12² - (4 * -1 * -20)
Δ = 144 - (4*20)
Δ = 144 - (80)
Δ = 64 Δ > 0
-x2-12x-20=0
x = -b ∓ √Δ 2a
x' = 12 - √64 2*-1 = 12 - 8.0 -2 = 4.0 -2 = -2.0
x" = 12 + √64 2*-1 = 12 + 8.0 -2 = 20.0 -2 = -10.0
x' = -2.0
x" = -10.0
S = {x ∈ R / x' = -2.0, x" = -10.0 }