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 = -24.0 30 = -0.8
x" = 13 + √1369 2*15 = 13 + 37.0 30 = 50.0 30 = 1.66666666667
x' = -180.0
x" = 375.0
S = {x ∈ R / x' = -180.0, x" = 375.0 }