-1x2 +20x -19 = 0
ax2 bx c = 0
a = -1
b = 20
c = -19
Δ = b2-4ac
Δ = 20² - (4 * -1 * -19)
Δ = 400 - (4*19)
Δ = 400 - (76)
Δ = 324 Δ > 0
-x2+20x-19=0
x = -b ∓ √Δ 2a
x' = -20 - √324 2*-1 = -20 - 18.0 -2 = -38.0 -2 = 19.0
x" = -20 + √324 2*-1 = -20 + 18.0 -2 = -2.0 -2 = 1.0
x' = 19.0
x" = 1.0
S = {x ∈ R / x' = 19.0, x" = 1.0 }