-1x2 +4x +12 = 0

ax2 bx c = 0

a = -1

b = 4

c = 12

Δ = b2-4ac

Δ = 4² - (4 * -1 * 12)

Δ = 16 - (4*-12)

Δ = 16 - (-48)

Δ = 64      Δ > 0

-x2+4x+12=0

x = -b ∓ √Δ 2a

x' = -4 - √64 2*-1 = -4 - 8.0 -2 = -12.0 -2 = 6.0

x" = -4 + √64 2*-1 = -4 + 8.0 -2 = 4.0 -2 = -2.0

x' = 6.0

x" = -2.0

S = {x ∈ R / x' = 6.0, x" = -2.0 }