-9x2 +13x -4 = 0
ax2 bx c = 0
a = -9
b = 13
c = -4
Δ = b2-4ac
Δ = 13² - (4 * -9 * -4)
Δ = 169 - (4*36)
Δ = 169 - (144)
Δ = 25 Δ > 0
-9x2+13x-4=0
x = -b ∓ √Δ 2a
x' = -13 - √25 2*-9 = -13 - 5.0 -18 = -18.0 -18 = 1.0
x" = -13 + √25 2*-9 = -13 + 5.0 -18 = -8.0 -18 = 0.444444444444
x' = 81.0
x" = 36.0
S = {x ∈ R / x' = 81.0, x" = 36.0 }