-1x2 +x +2 = 0
ax2 bx c = 0
a = -1
b = 1
c = 2
Δ = b2-4ac
Δ = ² - (4 * -1 * 2)
Δ = 1 - (4*-2)
Δ = 1 - (-8)
Δ = 9 Δ > 0
-x2+x+2=0
x = -b ∓ √Δ 2a
x' = -1 - √9 2*-1 = -1 - 3.0 -2 = -4.0 -2 = 2.0
x" = -1 + √9 2*-1 = -1 + 3.0 -2 = 2.0 -2 = -1.0
x' = 2.0
x" = -1.0
S = {x ∈ R / x' = 2.0, x" = -1.0 }