5x2 -19x -4 = 0
ax2 bx c = 0
a = 5
b = -19
c = -4
Δ = b2-4ac
Δ = -19² - (4 * 5 * -4)
Δ = 361 - (4*-20)
Δ = 361 - (-80)
Δ = 441 Δ > 0
5x2-19x-4=0
x = -b ∓ √Δ 2a
x' = 19 - √441 2*5 = 19 - 21.0 10 = -2.0 10 = -0.2
x" = 19 + √441 2*5 = 19 + 21.0 10 = 40.0 10 = 4.0
x' = -5.0
x" = 100.0
S = {x ∈ R / x' = -5.0, x" = 100.0 }