-4x2 +23x -15 = 0
ax2 bx c = 0
a = -4
b = 23
c = -15
Δ = b2-4ac
Δ = 23² - (4 * -4 * -15)
Δ = 529 - (4*60)
Δ = 529 - (240)
Δ = 289 Δ > 0
-4x2+23x-15=0
x = -b ∓ √Δ 2a
x' = -23 - √289 2*-4 = -23 - 17.0 -8 = -40.0 -8 = 5.0
x" = -23 + √289 2*-4 = -23 + 17.0 -8 = -6.0 -8 = 0.75
x' = 80.0
x" = 12.0
S = {x ∈ R / x' = 80.0, x" = 12.0 }