15x2 +21x +6 = 0
ax2 bx c = 0
a = 15
b = 21
c = 6
Δ = b2-4ac
Δ = 21² - (4 * 15 * 6)
Δ = 441 - (4*90)
Δ = 441 - (360)
Δ = 81 Δ > 0
15x2+21x+6=0
x = -b ∓ √Δ 2a
x' = -21 - √81 2*15 = -21 - 9.0 30 = -30.0 30 = -1.0
x" = -21 + √81 2*15 = -21 + 9.0 30 = -12.0 30 = -0.4
x' = -225.0
x" = -90.0
S = {x ∈ R / x' = -225.0, x" = -90.0 }