-1x2 +7x +8 = 0
ax2 bx c = 0
a = -1
b = 7
c = 8
Δ = b2-4ac
Δ = 7² - (4 * -1 * 8)
Δ = 49 - (4*-8)
Δ = 49 - (-32)
Δ = 81 Δ > 0
-x2+7x+8=0
x = -b ∓ √Δ 2a
x' = -7 - √81 2*-1 = -7 - 9.0 -2 = -16.0 -2 = 8.0
x" = -7 + √81 2*-1 = -7 + 9.0 -2 = 2.0 -2 = -1.0
x' = 8.0
x" = -1.0
S = {x ∈ R / x' = 8.0, x" = -1.0 }