-4x2 +5x +9 = 0
ax2 bx c = 0
a = -4
b = 5
c = 9
Δ = b2-4ac
Δ = 5² - (4 * -4 * 9)
Δ = 25 - (4*-36)
Δ = 25 - (-144)
Δ = 169 Δ > 0
-4x2+5x+9=0
x = -b ∓ √Δ 2a
x' = -5 - √169 2*-4 = -5 - 13.0 -8 = -18.0 -8 = 2.25
x" = -5 + √169 2*-4 = -5 + 13.0 -8 = 8.0 -8 = -1.0
x' = 36.0
x" = -16.0
S = {x ∈ R / x' = 36.0, x" = -16.0 }