-4x2 +4x +15 = 0
ax2 bx c = 0
a = -4
b = 4
c = 15
Δ = b2-4ac
Δ = 4² - (4 * -4 * 15)
Δ = 16 - (4*-60)
Δ = 16 - (-240)
Δ = 256 Δ > 0
-4x2+4x+15=0
x = -b ∓ √Δ 2a
x' = -4 - √256 2*-4 = -4 - 16.0 -8 = -20.0 -8 = 2.5
x" = -4 + √256 2*-4 = -4 + 16.0 -8 = 12.0 -8 = -1.5
x' = 40.0
x" = -24.0
S = {x ∈ R / x' = 40.0, x" = -24.0 }