-6x2 +21x -18 = 0
ax2 bx c = 0
a = -6
b = 21
c = -18
Δ = b2-4ac
Δ = 21² - (4 * -6 * -18)
Δ = 441 - (4*108)
Δ = 441 - (432)
Δ = 9 Δ > 0
-6x2+21x-18=0
x = -b ∓ √Δ 2a
x' = -21 - √9 2*-6 = -21 - 3.0 -12 = -24.0 -12 = 2.0
x" = -21 + √9 2*-6 = -21 + 3.0 -12 = -18.0 -12 = 1.5
x' = 72.0
x" = 54.0
S = {x ∈ R / x' = 72.0, x" = 54.0 }