-1x2 -8x +9 = 0
ax2 bx c = 0
a = -1
b = -8
c = 9
Δ = b2-4ac
Δ = -8² - (4 * -1 * 9)
Δ = 64 - (4*-9)
Δ = 64 - (-36)
Δ = 100 Δ > 0
-x2-8x+9=0
x = -b ∓ √Δ 2a
x' = 8 - √100 2*-1 = 8 - 10.0 -2 = -2.0 -2 = 1.0
x" = 8 + √100 2*-1 = 8 + 10.0 -2 = 18.0 -2 = -9.0
x' = 1.0
x" = -9.0
S = {x ∈ R / x' = 1.0, x" = -9.0 }