5x2 +20x +15 = 0
ax2 bx c = 0
a = 5
b = 20
c = 15
Δ = b2-4ac
Δ = 20² - (4 * 5 * 15)
Δ = 400 - (4*75)
Δ = 400 - (300)
Δ = 100 Δ > 0
5x2+20x+15=0
x = -b ∓ √Δ 2a
x' = -20 - √100 2*5 = -20 - 10.0 10 = -30.0 10 = -3.0
x" = -20 + √100 2*5 = -20 + 10.0 10 = -10.0 10 = -1.0
x' = -75.0
x" = -25.0
S = {x ∈ R / x' = -75.0, x" = -25.0 }