-1x2 -10x -9 = 0
ax2 bx c = 0
a = -1
b = -10
c = -9
Δ = b2-4ac
Δ = -10² - (4 * -1 * -9)
Δ = 100 - (4*9)
Δ = 100 - (36)
Δ = 64 Δ > 0
-x2-10x-9=0
x = -b ∓ √Δ 2a
x' = 10 - √64 2*-1 = 10 - 8.0 -2 = 2.0 -2 = -1.0
x" = 10 + √64 2*-1 = 10 + 8.0 -2 = 18.0 -2 = -9.0
x' = -1.0
x" = -9.0
S = {x ∈ R / x' = -1.0, x" = -9.0 }