-4x2 +16x +9 = 0
ax2 bx c = 0
a = -4
b = 16
c = 9
Δ = b2-4ac
Δ = 16² - (4 * -4 * 9)
Δ = 256 - (4*-36)
Δ = 256 - (-144)
Δ = 400 Δ > 0
-4x2+16x+9=0
x = -b ∓ √Δ 2a
x' = -16 - √400 2*-4 = -16 - 20.0 -8 = -36.0 -8 = 4.5
x" = -16 + √400 2*-4 = -16 + 20.0 -8 = 4.0 -8 = -0.5
x' = 72.0
x" = -8.0
S = {x ∈ R / x' = 72.0, x" = -8.0 }