-15x2 +7x +8 = 0
ax2 bx c = 0
a = -15
b = 7
c = 8
Δ = b2-4ac
Δ = 7² - (4 * -15 * 8)
Δ = 49 - (4*-120)
Δ = 49 - (-480)
Δ = 529 Δ > 0
-15x2+7x+8=0
x = -b ∓ √Δ 2a
x' = -7 - √529 2*-15 = -7 - 23.0 -30 = -30.0 -30 = 1.0
x" = -7 + √529 2*-15 = -7 + 23.0 -30 = 16.0 -30 = -0.533333333333
x' = 225.0
x" = -120.0
S = {x ∈ R / x' = 225.0, x" = -120.0 }