-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 = -30.0 -30 = 1.0
x" = -9 + √441 2*-15 = -9 + 21.0 -30 = 12.0 -30 = -0.4
x' = 225.0
x" = -90.0
S = {x ∈ R / x' = 225.0, x" = -90.0 }