-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 }