18x2 -x -5 = 0
ax2 bx c = 0
a = 18
b = -1
c = -5
Δ = b2-4ac
Δ = -² - (4 * 18 * -5)
Δ = 1 - (4*-90)
Δ = 1 - (-360)
Δ = 361 Δ > 0
18x2-x-5=0
x = -b ∓ √Δ 2a
x' = 1 - √361 2*18 = 1 - 19.0 36 = -18.0 36 = -0.5
x" = 1 + √361 2*18 = 1 + 19.0 36 = 20.0 36 = 0.555555555556
x' = -162.0
x" = 180.0
S = {x ∈ R / x' = -162.0, x" = 180.0 }