18x2 -7x -8 = 0
ax2 bx c = 0
a = 18
b = -7
c = -8
Δ = b2-4ac
Δ = -7² - (4 * 18 * -8)
Δ = 49 - (4*-144)
Δ = 49 - (-576)
Δ = 625 Δ > 0
18x2-7x-8=0
x = -b ∓ √Δ 2a
x' = 7 - √625 2*18 = 7 - 25.0 36 = -18.0 36 = -0.5
x" = 7 + √625 2*18 = 7 + 25.0 36 = 32.0 36 = 0.888888888889
x' = -162.0
x" = 288.0
S = {x ∈ R / x' = -162.0, x" = 288.0 }