5x2 -4x -9 = 0
ax2 bx c = 0
a = 5
b = -4
c = -9
Δ = b2-4ac
Δ = -4² - (4 * 5 * -9)
Δ = 16 - (4*-45)
Δ = 16 - (-180)
Δ = 196 Δ > 0
5x2-4x-9=0
x = -b ∓ √Δ 2a
x' = 4 - √196 2*5 = 4 - 14.0 10 = -10.0 10 = -1.0
x" = 4 + √196 2*5 = 4 + 14.0 10 = 18.0 10 = 1.8
x' = -25.0
x" = 45.0
S = {x ∈ R / x' = -25.0, x" = 45.0 }