5x2 +21x +4 = 0
ax2 bx c = 0
a = 5
b = 21
c = 4
Δ = b2-4ac
Δ = 21² - (4 * 5 * 4)
Δ = 441 - (4*20)
Δ = 441 - (80)
Δ = 361 Δ > 0
5x2+21x+4=0
x = -b ∓ √Δ 2a
x' = -21 - √361 2*5 = -21 - 19.0 10 = -40.0 10 = -4.0
x" = -21 + √361 2*5 = -21 + 19.0 10 = -2.0 10 = -0.2
x' = -100.0
x" = -5.0
S = {x ∈ R / x' = -100.0, x" = -5.0 }