5x2 -20x +15 = 0
ax2 bx c = 0
a = 5
b = -20
c = 15
Δ = b2-4ac
Δ = -20² - (4 * 5 * 15)
Δ = 400 - (4*75)
Δ = 400 - (300)
Δ = 100 Δ > 0
5x2-20x+15=0
x = -b ∓ √Δ 2a
x' = 20 - √100 2*5 = 20 - 10.0 10 = 10.0 10 = 1.0
x" = 20 + √100 2*5 = 20 + 10.0 10 = 30.0 10 = 3.0
x' = 25.0
x" = 75.0
S = {x ∈ R / x' = 25.0, x" = 75.0 }