-4x2 -19x -15 = 0
ax2 bx c = 0
a = -4
b = -19
c = -15
Δ = b2-4ac
Δ = -19² - (4 * -4 * -15)
Δ = 361 - (4*60)
Δ = 361 - (240)
Δ = 121 Δ > 0
-4x2-19x-15=0
x = -b ∓ √Δ 2a
x' = 19 - √121 2*-4 = 19 - 11.0 -8 = 8.0 -8 = -1.0
x" = 19 + √121 2*-4 = 19 + 11.0 -8 = 30.0 -8 = -3.75
x' = -16.0
x" = -60.0
S = {x ∈ R / x' = -16.0, x" = -60.0 }