-4x2 +11x +15 = 0
ax2 bx c = 0
a = -4
b = 11
c = 15
Δ = b2-4ac
Δ = 11² - (4 * -4 * 15)
Δ = 121 - (4*-60)
Δ = 121 - (-240)
Δ = 361 Δ > 0
-4x2+11x+15=0
x = -b ∓ √Δ 2a
x' = -11 - √361 2*-4 = -11 - 19.0 -8 = -30.0 -8 = 3.75
x" = -11 + √361 2*-4 = -11 + 19.0 -8 = 8.0 -8 = -1.0
x' = 60.0
x" = -16.0
S = {x ∈ R / x' = 60.0, x" = -16.0 }