-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 = -14.0 -12 = 1.16666666667
x" = 11 + √625 2*-6 = 11 + 25.0 -12 = 36.0 -12 = -3.0
x' = 42.0
x" = -108.0
S = {x ∈ R / x' = 42.0, x" = -108.0 }