-1x2 -20x -19 = 0
ax2 bx c = 0
a = -1
b = -20
c = -19
Δ = b2-4ac
Δ = -20² - (4 * -1 * -19)
Δ = 400 - (4*19)
Δ = 400 - (76)
Δ = 324 Δ > 0
-x2-20x-19=0
x = -b ∓ √Δ 2a
x' = 20 - √324 2*-1 = 20 - 18.0 -2 = 2.0 -2 = -1.0
x" = 20 + √324 2*-1 = 20 + 18.0 -2 = 38.0 -2 = -19.0
x' = -1.0
x" = -19.0
S = {x ∈ R / x' = -1.0, x" = -19.0 }