15x2 +13x -20 = 0
ax2 bx c = 0
a = 15
b = 13
c = -20
Δ = b2-4ac
Δ = 13² - (4 * 15 * -20)
Δ = 169 - (4*-300)
Δ = 169 - (-1200)
Δ = 1369 Δ > 0
15x2+13x-20=0
x = -b ∓ √Δ 2a
x' = -13 - √1369 2*15 = -13 - 37.0 30 = -50.0 30 = -1.66666666667
x" = -13 + √1369 2*15 = -13 + 37.0 30 = 24.0 30 = 0.8
x' = -375.0
x" = 180.0
S = {x ∈ R / x' = -375.0, x" = 180.0 }