5x2 -13x -18 = 0
ax2 bx c = 0
a = 5
b = -13
c = -18
Δ = b2-4ac
Δ = -13² - (4 * 5 * -18)
Δ = 169 - (4*-90)
Δ = 169 - (-360)
Δ = 529 Δ > 0
5x2-13x-18=0
x = -b ∓ √Δ 2a
x' = 13 - √529 2*5 = 13 - 23.0 10 = -10.0 10 = -1.0
x" = 13 + √529 2*5 = 13 + 23.0 10 = 36.0 10 = 3.6
x' = -25.0
x" = 90.0
S = {x ∈ R / x' = -25.0, x" = 90.0 }