-6x2 +9x +15 = 0
ax2 bx c = 0
a = -6
b = 9
c = 15
Δ = b2-4ac
Δ = 9² - (4 * -6 * 15)
Δ = 81 - (4*-90)
Δ = 81 - (-360)
Δ = 441 Δ > 0
-6x2+9x+15=0
x = -b ∓ √Δ 2a
x' = -9 - √441 2*-6 = -9 - 21.0 -12 = -30.0 -12 = 2.5
x" = -9 + √441 2*-6 = -9 + 21.0 -12 = 12.0 -12 = -1.0
x' = 90.0
x" = -36.0
S = {x ∈ R / x' = 90.0, x" = -36.0 }