-12x2 +21x -9 = 0
ax2 bx c = 0
a = -12
b = 21
c = -9
Δ = b2-4ac
Δ = 21² - (4 * -12 * -9)
Δ = 441 - (4*108)
Δ = 441 - (432)
Δ = 9 Δ > 0
-12x2+21x-9=0
x = -b ∓ √Δ 2a
x' = -21 - √9 2*-12 = -21 - 3.0 -24 = -24.0 -24 = 1.0
x" = -21 + √9 2*-12 = -21 + 3.0 -24 = -18.0 -24 = 0.75
x' = 144.0
x" = 108.0
S = {x ∈ R / x' = 144.0, x" = 108.0 }