-1x2 -8x -15 = 0
ax2 bx c = 0
a = -1
b = -8
c = -15
Δ = b2-4ac
Δ = -8² - (4 * -1 * -15)
Δ = 64 - (4*15)
Δ = 64 - (60)
Δ = 4 Δ > 0
-x2-8x-15=0
x = -b ∓ √Δ 2a
x' = 8 - √4 2*-1 = 8 - 2.0 -2 = 6.0 -2 = -3.0
x" = 8 + √4 2*-1 = 8 + 2.0 -2 = 10.0 -2 = -5.0
x' = -3.0
x" = -5.0
S = {x ∈ R / x' = -3.0, x" = -5.0 }