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 = -30.0 10 = -3.0
x" = -9 + √441 2*5 = -9 + 21.0 10 = 12.0 10 = 1.2
x' = -75.0
x" = 30.0
S = {x ∈ R / x' = -75.0, x" = 30.0 }