-15x2 +21x +18 = 0
ax2 bx c = 0
a = -15
b = 21
c = 18
Δ = b2-4ac
Δ = 21² - (4 * -15 * 18)
Δ = 441 - (4*-270)
Δ = 441 - (-1080)
Δ = 1521 Δ > 0
-15x2+21x+18=0
x = -b ∓ √Δ 2a
x' = -21 - √1521 2*-15 = -21 - 39.0 -30 = -60.0 -30 = 2.0
x" = -21 + √1521 2*-15 = -21 + 39.0 -30 = 18.0 -30 = -0.6
x' = 450.0
x" = -135.0
S = {x ∈ R / x' = 450.0, x" = -135.0 }