5x2 -9x -18 = 0
ax2 bx c = 0
a = 5
b = -9
c = -18
Δ = b2-4ac
Δ = -9² - (4 * 5 * -18)
Δ = 81 - (4*-90)
Δ = 81 - (-360)
Δ = 441 Δ > 0
5x2-9x-18=0
x = -b ∓ √Δ 2a
x' = 9 - √441 2*5 = 9 - 21.0 10 = -12.0 10 = -1.2
x" = 9 + √441 2*5 = 9 + 21.0 10 = 30.0 10 = 3.0
x' = -30.0
x" = 75.0
S = {x ∈ R / x' = -30.0, x" = 75.0 }