-12x2 +4x +21 = 0
ax2 bx c = 0
a = -12
b = 4
c = 21
Δ = b2-4ac
Δ = 4² - (4 * -12 * 21)
Δ = 16 - (4*-252)
Δ = 16 - (-1008)
Δ = 1024 Δ > 0
-12x2+4x+21=0
x = -b ∓ √Δ 2a
x' = -4 - √1024 2*-12 = -4 - 32.0 -24 = -36.0 -24 = 1.5
x" = -4 + √1024 2*-12 = -4 + 32.0 -24 = 28.0 -24 = -1.16666666667
x' = 216.0
x" = -168.0
S = {x ∈ R / x' = 216.0, x" = -168.0 }