-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 = -30.0 -30 = 1.0
x" = -6 + √576 2*-15 = -6 + 24.0 -30 = 18.0 -30 = -0.6
x' = 225.0
x" = -135.0
S = {x ∈ R / x' = 225.0, x" = -135.0 }