-9x2 +11x +20 = 0
ax2 bx c = 0
a = -9
b = 11
c = 20
Δ = b2-4ac
Δ = 11² - (4 * -9 * 20)
Δ = 121 - (4*-180)
Δ = 121 - (-720)
Δ = 841 Δ > 0
-9x2+11x+20=0
x = -b ∓ √Δ 2a
x' = -11 - √841 2*-9 = -11 - 29.0 -18 = -40.0 -18 = 2.22222222222
x" = -11 + √841 2*-9 = -11 + 29.0 -18 = 18.0 -18 = -1.0
x' = 180.0
x" = -81.0
S = {x ∈ R / x' = 180.0, x" = -81.0 }