5x2 -x -4 = 0
ax2 bx c = 0
a = 5
b = -1
c = -4
Δ = b2-4ac
Δ = -² - (4 * 5 * -4)
Δ = 1 - (4*-20)
Δ = 1 - (-80)
Δ = 81 Δ > 0
5x2-x-4=0
x = -b ∓ √Δ 2a
x' = 1 - √81 2*5 = 1 - 9.0 10 = -8.0 10 = -0.8
x" = 1 + √81 2*5 = 1 + 9.0 10 = 10.0 10 = 1.0
x' = -20.0
x" = 25.0
S = {x ∈ R / x' = -20.0, x" = 25.0 }