-9x2 +4x +13 = 0
ax2 bx c = 0
a = -9
b = 4
c = 13
Δ = b2-4ac
Δ = 4² - (4 * -9 * 13)
Δ = 16 - (4*-117)
Δ = 16 - (-468)
Δ = 484 Δ > 0
-9x2+4x+13=0
x = -b ∓ √Δ 2a
x' = -4 - √484 2*-9 = -4 - 22.0 -18 = -26.0 -18 = 1.44444444444
x" = -4 + √484 2*-9 = -4 + 22.0 -18 = 18.0 -18 = -1.0
x' = 117.0
x" = -81.0
S = {x ∈ R / x' = 117.0, x" = -81.0 }