15x2 -9x -6 = 0
ax2 bx c = 0
a = 15
b = -9
c = -6
Δ = b2-4ac
Δ = -9² - (4 * 15 * -6)
Δ = 81 - (4*-90)
Δ = 81 - (-360)
Δ = 441 Δ > 0
15x2-9x-6=0
x = -b ∓ √Δ 2a
x' = 9 - √441 2*15 = 9 - 21.0 30 = -12.0 30 = -0.4
x" = 9 + √441 2*15 = 9 + 21.0 30 = 30.0 30 = 1.0
x' = -90.0
x" = 225.0
S = {x ∈ R / x' = -90.0, x" = 225.0 }