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 = -32.0 36 = -0.888888888889
x" = -7 + √625 2*18 = -7 + 25.0 36 = 18.0 36 = 0.5
x' = -288.0
x" = 162.0
S = {x ∈ R / x' = -288.0, x" = 162.0 }