-1x2 +17x +18 = 0
ax2 bx c = 0
a = -1
b = 17
c = 18
Δ = b2-4ac
Δ = 17² - (4 * -1 * 18)
Δ = 289 - (4*-18)
Δ = 289 - (-72)
Δ = 361 Δ > 0
-x2+17x+18=0
x = -b ∓ √Δ 2a
x' = -17 - √361 2*-1 = -17 - 19.0 -2 = -36.0 -2 = 18.0
x" = -17 + √361 2*-1 = -17 + 19.0 -2 = 2.0 -2 = -1.0
x' = 18.0
x" = -1.0
S = {x ∈ R / x' = 18.0, x" = -1.0 }