-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 = -18.0 -2 = 9.0
x" = -8 + √100 2*-1 = -8 + 10.0 -2 = 2.0 -2 = -1.0
x' = 9.0
x" = -1.0
S = {x ∈ R / x' = 9.0, x" = -1.0 }