-9x2 +10x +19 = 0
ax2 bx c = 0
a = -9
b = 10
c = 19
Δ = b2-4ac
Δ = 10² - (4 * -9 * 19)
Δ = 100 - (4*-171)
Δ = 100 - (-684)
Δ = 784 Δ > 0
-9x2+10x+19=0
x = -b ∓ √Δ 2a
x' = -10 - √784 2*-9 = -10 - 28.0 -18 = -38.0 -18 = 2.11111111111
x" = -10 + √784 2*-9 = -10 + 28.0 -18 = 18.0 -18 = -1.0
x' = 171.0
x" = -81.0
S = {x ∈ R / x' = 171.0, x" = -81.0 }