-9x2 +8x +20 = 0
ax2 bx c = 0
a = -9
b = 8
c = 20
Δ = b2-4ac
Δ = 8² - (4 * -9 * 20)
Δ = 64 - (4*-180)
Δ = 64 - (-720)
Δ = 784 Δ > 0
-9x2+8x+20=0
x = -b ∓ √Δ 2a
x' = -8 - √784 2*-9 = -8 - 28.0 -18 = -36.0 -18 = 2.0
x" = -8 + √784 2*-9 = -8 + 28.0 -18 = 20.0 -18 = -1.11111111111
x' = 162.0
x" = -90.0
S = {x ∈ R / x' = 162.0, x" = -90.0 }