-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 = -10.0 -8 = 1.25
x" = 11 + √441 2*-4 = 11 + 21.0 -8 = 32.0 -8 = -4.0
x' = 20.0
x" = -64.0
S = {x ∈ R / x' = 20.0, x" = -64.0 }