-1x2 -7x +18 = 0
ax2 bx c = 0
a = -1
b = -7
c = 18
Δ = b2-4ac
Δ = -7² - (4 * -1 * 18)
Δ = 49 - (4*-18)
Δ = 49 - (-72)
Δ = 121 Δ > 0
-x2-7x+18=0
x = -b ∓ √Δ 2a
x' = 7 - √121 2*-1 = 7 - 11.0 -2 = -4.0 -2 = 2.0
x" = 7 + √121 2*-1 = 7 + 11.0 -2 = 18.0 -2 = -9.0
x' = 2.0
x" = -9.0
S = {x ∈ R / x' = 2.0, x" = -9.0 }