-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 = -18.0 -36 = 0.5
x" = -1 + √289 2*-18 = -1 + 17.0 -36 = 16.0 -36 = -0.444444444444
x' = 162.0
x" = -144.0
S = {x ∈ R / x' = 162.0, x" = -144.0 }