-1x2 +8x +20 = 0
ax2 bx c = 0
a = -1
b = 8
c = 20
Δ = b2-4ac
Δ = 8² - (4 * -1 * 20)
Δ = 64 - (4*-20)
Δ = 64 - (-80)
Δ = 144 Δ > 0
-x2+8x+20=0
x = -b ∓ √Δ 2a
x' = -8 - √144 2*-1 = -8 - 12.0 -2 = -20.0 -2 = 10.0
x" = -8 + √144 2*-1 = -8 + 12.0 -2 = 4.0 -2 = -2.0
x' = 10.0
x" = -2.0
S = {x ∈ R / x' = 10.0, x" = -2.0 }