-4x2 -15x -9 = 0
ax2 bx c = 0
a = -4
b = -15
c = -9
Δ = b2-4ac
Δ = -15² - (4 * -4 * -9)
Δ = 225 - (4*36)
Δ = 225 - (144)
Δ = 81 Δ > 0
-4x2-15x-9=0
x = -b ∓ √Δ 2a
x' = 15 - √81 2*-4 = 15 - 9.0 -8 = 6.0 -8 = -0.75
x" = 15 + √81 2*-4 = 15 + 9.0 -8 = 24.0 -8 = -3.0
x' = -12.0
x" = -48.0
S = {x ∈ R / x' = -12.0, x" = -48.0 }