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 }