5x2 +15x -20 = 0
ax2 bx c = 0
a = 5
b = 15
c = -20
Δ = b2-4ac
Δ = 15² - (4 * 5 * -20)
Δ = 225 - (4*-100)
Δ = 225 - (-400)
Δ = 625 Δ > 0
5x2+15x-20=0
x = -b ∓ √Δ 2a
x' = -15 - √625 2*5 = -15 - 25.0 10 = -40.0 10 = -4.0
x" = -15 + √625 2*5 = -15 + 25.0 10 = 10.0 10 = 1.0
x' = -100.0
x" = 25.0
S = {x ∈ R / x' = -100.0, x" = 25.0 }