-1x2 +4x +5 = 0
ax2 bx c = 0
a = -1
b = 4
c = 5
Δ = b2-4ac
Δ = 4² - (4 * -1 * 5)
Δ = 16 - (4*-5)
Δ = 16 - (-20)
Δ = 36 Δ > 0
-x2+4x+5=0
x = -b ∓ √Δ 2a
x' = -4 - √36 2*-1 = -4 - 6.0 -2 = -10.0 -2 = 5.0
x" = -4 + √36 2*-1 = -4 + 6.0 -2 = 2.0 -2 = -1.0
x' = 5.0
x" = -1.0
S = {x ∈ R / x' = 5.0, x" = -1.0 }