-1x2 -x +20 = 0
ax2 bx c = 0
a = -1
b = -1
c = 20
Δ = b2-4ac
Δ = -² - (4 * -1 * 20)
Δ = 1 - (4*-20)
Δ = 1 - (-80)
Δ = 81 Δ > 0
-x2-x+20=0
x = -b ∓ √Δ 2a
x' = 1 - √81 2*-1 = 1 - 9.0 -2 = -8.0 -2 = 4.0
x" = 1 + √81 2*-1 = 1 + 9.0 -2 = 10.0 -2 = -5.0
x' = 4.0
x" = -5.0
S = {x ∈ R / x' = 4.0, x" = -5.0 }