-9x2 -x +8 = 0
ax2 bx c = 0
a = -9
b = -1
c = 8
Δ = b2-4ac
Δ = -² - (4 * -9 * 8)
Δ = 1 - (4*-72)
Δ = 1 - (-288)
Δ = 289 Δ > 0
-9x2-x+8=0
x = -b ∓ √Δ 2a
x' = 1 - √289 2*-9 = 1 - 17.0 -18 = -16.0 -18 = 0.888888888889
x" = 1 + √289 2*-9 = 1 + 17.0 -18 = 18.0 -18 = -1.0
x' = 72.0
x" = -81.0
S = {x ∈ R / x' = 72.0, x" = -81.0 }