-1x2 +3x +18 = 0
ax2 bx c = 0
a = -1
b = 3
c = 18
Δ = b2-4ac
Δ = 3² - (4 * -1 * 18)
Δ = 9 - (4*-18)
Δ = 9 - (-72)
Δ = 81 Δ > 0
-x2+3x+18=0
x = -b ∓ √Δ 2a
x' = -3 - √81 2*-1 = -3 - 9.0 -2 = -12.0 -2 = 6.0
x" = -3 + √81 2*-1 = -3 + 9.0 -2 = 6.0 -2 = -3.0
x' = 6.0
x" = -3.0
S = {x ∈ R / x' = 6.0, x" = -3.0 }