5x2 -x -18 = 0
ax2 bx c = 0
a = 5
b = -1
c = -18
Δ = b2-4ac
Δ = -² - (4 * 5 * -18)
Δ = 1 - (4*-90)
Δ = 1 - (-360)
Δ = 361 Δ > 0
5x2-x-18=0
x = -b ∓ √Δ 2a
x' = 1 - √361 2*5 = 1 - 19.0 10 = -18.0 10 = -1.8
x" = 1 + √361 2*5 = 1 + 19.0 10 = 20.0 10 = 2.0
x' = -45.0
x" = 50.0
S = {x ∈ R / x' = -45.0, x" = 50.0 }