-4x2 +21x +18 = 0
ax2 bx c = 0
a = -4
b = 21
c = 18
Δ = b2-4ac
Δ = 21² - (4 * -4 * 18)
Δ = 441 - (4*-72)
Δ = 441 - (-288)
Δ = 729 Δ > 0
-4x2+21x+18=0
x = -b ∓ √Δ 2a
x' = -21 - √729 2*-4 = -21 - 27.0 -8 = -48.0 -8 = 6.0
x" = -21 + √729 2*-4 = -21 + 27.0 -8 = 6.0 -8 = -0.75
x' = 96.0
x" = -12.0
S = {x ∈ R / x' = 96.0, x" = -12.0 }