-4x2 +19x +5 = 0
ax2 bx c = 0
a = -4
b = 19
c = 5
Δ = b2-4ac
Δ = 19² - (4 * -4 * 5)
Δ = 361 - (4*-20)
Δ = 361 - (-80)
Δ = 441 Δ > 0
-4x2+19x+5=0
x = -b ∓ √Δ 2a
x' = -19 - √441 2*-4 = -19 - 21.0 -8 = -40.0 -8 = 5.0
x" = -19 + √441 2*-4 = -19 + 21.0 -8 = 2.0 -8 = -0.25
x' = 80.0
x" = -4.0
S = {x ∈ R / x' = 80.0, x" = -4.0 }