18x2 -x -4 = 0
ax2 bx c = 0
a = 18
b = -1
c = -4
Δ = b2-4ac
Δ = -² - (4 * 18 * -4)
Δ = 1 - (4*-72)
Δ = 1 - (-288)
Δ = 289 Δ > 0
18x2-x-4=0
x = -b ∓ √Δ 2a
x' = 1 - √289 2*18 = 1 - 17.0 36 = -16.0 36 = -0.444444444444
x" = 1 + √289 2*18 = 1 + 17.0 36 = 18.0 36 = 0.5
x' = -144.0
x" = 162.0
S = {x ∈ R / x' = -144.0, x" = 162.0 }