-6x2 +11x +21 = 0
ax2 bx c = 0
a = -6
b = 11
c = 21
Δ = b2-4ac
Δ = 11² - (4 * -6 * 21)
Δ = 121 - (4*-126)
Δ = 121 - (-504)
Δ = 625 Δ > 0
-6x2+11x+21=0
x = -b ∓ √Δ 2a
x' = -11 - √625 2*-6 = -11 - 25.0 -12 = -36.0 -12 = 3.0
x" = -11 + √625 2*-6 = -11 + 25.0 -12 = 14.0 -12 = -1.16666666667
x' = 108.0
x" = -42.0
S = {x ∈ R / x' = 108.0, x" = -42.0 }