-4x2 +7x +15 = 0
ax2 bx c = 0
a = -4
b = 7
c = 15
Δ = b2-4ac
Δ = 7² - (4 * -4 * 15)
Δ = 49 - (4*-60)
Δ = 49 - (-240)
Δ = 289 Δ > 0
-4x2+7x+15=0
x = -b ∓ √Δ 2a
x' = -7 - √289 2*-4 = -7 - 17.0 -8 = -24.0 -8 = 3.0
x" = -7 + √289 2*-4 = -7 + 17.0 -8 = 10.0 -8 = -1.25
x' = 48.0
x" = -20.0
S = {x ∈ R / x' = 48.0, x" = -20.0 }