-8x2 +7x +18 = 0
ax2 bx c = 0
a = -8
b = 7
c = 18
Δ = b2-4ac
Δ = 7² - (4 * -8 * 18)
Δ = 49 - (4*-144)
Δ = 49 - (-576)
Δ = 625 Δ > 0
-8x2+7x+18=0
x = -b ∓ √Δ 2a
x' = -7 - √625 2*-8 = -7 - 25.0 -16 = -32.0 -16 = 2.0
x" = -7 + √625 2*-8 = -7 + 25.0 -16 = 18.0 -16 = -1.125
x' = 128.0
x" = -72.0
S = {x ∈ R / x' = 128.0, x" = -72.0 }