-6x2 -5x +21 = 0
ax2 bx c = 0
a = -6
b = -5
c = 21
Δ = b2-4ac
Δ = -5² - (4 * -6 * 21)
Δ = 25 - (4*-126)
Δ = 25 - (-504)
Δ = 529 Δ > 0
-6x2-5x+21=0
x = -b ∓ √Δ 2a
x' = 5 - √529 2*-6 = 5 - 23.0 -12 = -18.0 -12 = 1.5
x" = 5 + √529 2*-6 = 5 + 23.0 -12 = 28.0 -12 = -2.33333333333
x' = 54.0
x" = -84.0
S = {x ∈ R / x' = 54.0, x" = -84.0 }