5x2 +21x -20 = 0
ax2 bx c = 0
a = 5
b = 21
c = -20
Δ = b2-4ac
Δ = 21² - (4 * 5 * -20)
Δ = 441 - (4*-100)
Δ = 441 - (-400)
Δ = 841 Δ > 0
5x2+21x-20=0
x = -b ∓ √Δ 2a
x' = -21 - √841 2*5 = -21 - 29.0 10 = -50.0 10 = -5.0
x" = -21 + √841 2*5 = -21 + 29.0 10 = 8.0 10 = 0.8
x' = -125.0
x" = 20.0
S = {x ∈ R / x' = -125.0, x" = 20.0 }