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 = -10.0 2 = -5.0
x" = -1 + √81 2*1 = -1 + 9.0 2 = 8.0 2 = 4.0
x' = -5.0
x" = 4.0
S = {x ∈ R / x' = -5.0, x" = 4.0 }