-9x2 +8x +1 = 0
ax2 bx c = 0
a = -9
b = 8
c = 1
Δ = b2-4ac
Δ = 8² - (4 * -9 * 1)
Δ = 64 - (4*-9)
Δ = 64 - (-36)
Δ = 100 Δ > 0
-9x2+8x+1=0
x = -b ∓ √Δ 2a
x' = -8 - √100 2*-9 = -8 - 10.0 -18 = -18.0 -18 = 1.0
x" = -8 + √100 2*-9 = -8 + 10.0 -18 = 2.0 -18 = -0.111111111111
x' = 81.0
x" = -9.0
S = {x ∈ R / x' = 81.0, x" = -9.0 }