15x2 -6x -9 = 0
ax2 bx c = 0
a = 15
b = -6
c = -9
Δ = b2-4ac
Δ = -6² - (4 * 15 * -9)
Δ = 36 - (4*-135)
Δ = 36 - (-540)
Δ = 576 Δ > 0
15x2-6x-9=0
x = -b ∓ √Δ 2a
x' = 6 - √576 2*15 = 6 - 24.0 30 = -18.0 30 = -0.6
x" = 6 + √576 2*15 = 6 + 24.0 30 = 30.0 30 = 1.0
x' = -135.0
x" = 225.0
S = {x ∈ R / x' = -135.0, x" = 225.0 }