-1x2 +8x -15 = 0
ax2 bx c = 0
a = -1
b = 8
c = -15
Δ = b2-4ac
Δ = 8² - (4 * -1 * -15)
Δ = 64 - (4*15)
Δ = 64 - (60)
Δ = 4 Δ > 0
-x2+8x-15=0
x = -b ∓ √Δ 2a
x' = -8 - √4 2*-1 = -8 - 2.0 -2 = -10.0 -2 = 5.0
x" = -8 + √4 2*-1 = -8 + 2.0 -2 = -6.0 -2 = 3.0
x' = 5.0
x" = 3.0
S = {x ∈ R / x' = 5.0, x" = 3.0 }