-1x2 +2x +8 = 0
ax2 bx c = 0
a = -1
b = 2
c = 8
Δ = b2-4ac
Δ = 2² - (4 * -1 * 8)
Δ = 4 - (4*-8)
Δ = 4 - (-32)
Δ = 36 Δ > 0
-x2+2x+8=0
x = -b ∓ √Δ 2a
x' = -2 - √36 2*-1 = -2 - 6.0 -2 = -8.0 -2 = 4.0
x" = -2 + √36 2*-1 = -2 + 6.0 -2 = 4.0 -2 = -2.0
x' = 4.0
x" = -2.0
S = {x ∈ R / x' = 4.0, x" = -2.0 }