-9x2 +4x +5 = 0
ax2 bx c = 0
a = -9
b = 4
c = 5
Δ = b2-4ac
Δ = 4² - (4 * -9 * 5)
Δ = 16 - (4*-45)
Δ = 16 - (-180)
Δ = 196 Δ > 0
-9x2+4x+5=0
x = -b ∓ √Δ 2a
x' = -4 - √196 2*-9 = -4 - 14.0 -18 = -18.0 -18 = 1.0
x" = -4 + √196 2*-9 = -4 + 14.0 -18 = 10.0 -18 = -0.555555555556
x' = 81.0
x" = -45.0
S = {x ∈ R / x' = 81.0, x" = -45.0 }