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 }