-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 = -4.0 -2 = 2.0
x" = 8 + √144 2*-1 = 8 + 12.0 -2 = 20.0 -2 = -10.0
x' = 2.0
x" = -10.0
S = {x ∈ R / x' = 2.0, x" = -10.0 }