-1x2 +11x -18 = 0
ax2 bx c = 0
a = -1
b = 11
c = -18
Δ = b2-4ac
Δ = 11² - (4 * -1 * -18)
Δ = 121 - (4*18)
Δ = 121 - (72)
Δ = 49 Δ > 0
-x2+11x-18=0
x = -b ∓ √Δ 2a
x' = -11 - √49 2*-1 = -11 - 7.0 -2 = -18.0 -2 = 9.0
x" = -11 + √49 2*-1 = -11 + 7.0 -2 = -4.0 -2 = 2.0
x' = 9.0
x" = 2.0
S = {x ∈ R / x' = 9.0, x" = 2.0 }