-18x2 -11x -1 = 0
ax2 bx c = 0
a = -18
b = -11
c = -1
Δ = b2-4ac
Δ = -11² - (4 * -18 * -1)
Δ = 121 - (4*18)
Δ = 121 - (72)
Δ = 49 Δ > 0
-18x2-11x-1=0
x = -b ∓ √Δ 2a
x' = 11 - √49 2*-18 = 11 - 7.0 -36 = 4.0 -36 = -0.111111111111
x" = 11 + √49 2*-18 = 11 + 7.0 -36 = 18.0 -36 = -0.5
x' = -36.0
x" = -162.0
S = {x ∈ R / x' = -36.0, x" = -162.0 }