15x2 +20x -20 = 0
ax2 bx c = 0
a = 15
b = 20
c = -20
Δ = b2-4ac
Δ = 20² - (4 * 15 * -20)
Δ = 400 - (4*-300)
Δ = 400 - (-1200)
Δ = 1600 Δ > 0
15x2+20x-20=0
x = -b ∓ √Δ 2a
x' = -20 - √1600 2*15 = -20 - 40.0 30 = -60.0 30 = -2.0
x" = -20 + √1600 2*15 = -20 + 40.0 30 = 20.0 30 = 0.666666666667
x' = -450.0
x" = 150.0
S = {x ∈ R / x' = -450.0, x" = 150.0 }