18x2 +5x -7 = 0
ax2 bx c = 0
a = 18
b = 5
c = -7
Δ = b2-4ac
Δ = 5² - (4 * 18 * -7)
Δ = 25 - (4*-126)
Δ = 25 - (-504)
Δ = 529 Δ > 0
18x2+5x-7=0
x = -b ∓ √Δ 2a
x' = -5 - √529 2*18 = -5 - 23.0 36 = -28.0 36 = -0.777777777778
x" = -5 + √529 2*18 = -5 + 23.0 36 = 18.0 36 = 0.5
x' = -252.0
x" = 162.0
S = {x ∈ R / x' = -252.0, x" = 162.0 }