-4x2 +11x +20 = 0
ax2 bx c = 0
a = -4
b = 11
c = 20
Δ = b2-4ac
Δ = 11² - (4 * -4 * 20)
Δ = 121 - (4*-80)
Δ = 121 - (-320)
Δ = 441 Δ > 0
-4x2+11x+20=0
x = -b ∓ √Δ 2a
x' = -11 - √441 2*-4 = -11 - 21.0 -8 = -32.0 -8 = 4.0
x" = -11 + √441 2*-4 = -11 + 21.0 -8 = 10.0 -8 = -1.25
x' = 64.0
x" = -20.0
S = {x ∈ R / x' = 64.0, x" = -20.0 }