18x2 +7x -1 = 0
ax2 bx c = 0
a = 18
b = 7
c = -1
Δ = b2-4ac
Δ = 7² - (4 * 18 * -1)
Δ = 49 - (4*-18)
Δ = 49 - (-72)
Δ = 121 Δ > 0
18x2+7x-1=0
x = -b ∓ √Δ 2a
x' = -7 - √121 2*18 = -7 - 11.0 36 = -18.0 36 = -0.5
x" = -7 + √121 2*18 = -7 + 11.0 36 = 4.0 36 = 0.111111111111
x' = -162.0
x" = 36.0
S = {x ∈ R / x' = -162.0, x" = 36.0 }