-1x2 +9x -18 = 0
ax2 bx c = 0
a = -1
b = 9
c = -18
Δ = b2-4ac
Δ = 9² - (4 * -1 * -18)
Δ = 81 - (4*18)
Δ = 81 - (72)
Δ = 9 Δ > 0
-x2+9x-18=0
x = -b ∓ √Δ 2a
x' = -9 - √9 2*-1 = -9 - 3.0 -2 = -12.0 -2 = 6.0
x" = -9 + √9 2*-1 = -9 + 3.0 -2 = -6.0 -2 = 3.0
x' = 6.0
x" = 3.0
S = {x ∈ R / x' = 6.0, x" = 3.0 }