5x2 -18x +9 = 0
ax2 bx c = 0
a = 5
b = -18
c = 9
Δ = b2-4ac
Δ = -18² - (4 * 5 * 9)
Δ = 324 - (4*45)
Δ = 324 - (180)
Δ = 144 Δ > 0
5x2-18x+9=0
x = -b ∓ √Δ 2a
x' = 18 - √144 2*5 = 18 - 12.0 10 = 6.0 10 = 0.6
x" = 18 + √144 2*5 = 18 + 12.0 10 = 30.0 10 = 3.0
x' = 15.0
x" = 75.0
S = {x ∈ R / x' = 15.0, x" = 75.0 }