-1x2 -2x +15 = 0
ax2 bx c = 0
a = -1
b = -2
c = 15
Δ = b2-4ac
Δ = -2² - (4 * -1 * 15)
Δ = 4 - (4*-15)
Δ = 4 - (-60)
Δ = 64 Δ > 0
-x2-2x+15=0
x = -b ∓ √Δ 2a
x' = 2 - √64 2*-1 = 2 - 8.0 -2 = -6.0 -2 = 3.0
x" = 2 + √64 2*-1 = 2 + 8.0 -2 = 10.0 -2 = -5.0
x' = 3.0
x" = -5.0
S = {x ∈ R / x' = 3.0, x" = -5.0 }