-1x2 +19x -18 = 0
ax2 bx c = 0
a = -1
b = 19
c = -18
Δ = b2-4ac
Δ = 19² - (4 * -1 * -18)
Δ = 361 - (4*18)
Δ = 361 - (72)
Δ = 289 Δ > 0
-x2+19x-18=0
x = -b ∓ √Δ 2a
x' = -19 - √289 2*-1 = -19 - 17.0 -2 = -36.0 -2 = 18.0
x" = -19 + √289 2*-1 = -19 + 17.0 -2 = -2.0 -2 = 1.0
x' = 18.0
x" = 1.0
S = {x ∈ R / x' = 18.0, x" = 1.0 }