-9x2 +20x -11 = 0
ax2 bx c = 0
a = -9
b = 20
c = -11
Δ = b2-4ac
Δ = 20² - (4 * -9 * -11)
Δ = 400 - (4*99)
Δ = 400 - (396)
Δ = 4 Δ > 0
-9x2+20x-11=0
x = -b ∓ √Δ 2a
x' = -20 - √4 2*-9 = -20 - 2.0 -18 = -22.0 -18 = 1.22222222222
x" = -20 + √4 2*-9 = -20 + 2.0 -18 = -18.0 -18 = 1.0
x' = 99.0
x" = 81.0
S = {x ∈ R / x' = 99.0, x" = 81.0 }