18x2 +11x -7 = 0
ax2 bx c = 0
a = 18
b = 11
c = -7
Δ = b2-4ac
Δ = 11² - (4 * 18 * -7)
Δ = 121 - (4*-126)
Δ = 121 - (-504)
Δ = 625 Δ > 0
18x2+11x-7=0
x = -b ∓ √Δ 2a
x' = -11 - √625 2*18 = -11 - 25.0 36 = -36.0 36 = -1.0
x" = -11 + √625 2*18 = -11 + 25.0 36 = 14.0 36 = 0.388888888889
x' = -324.0
x" = 126.0
S = {x ∈ R / x' = -324.0, x" = 126.0 }