-6x2 +7x +20 = 0
ax2 bx c = 0
a = -6
b = 7
c = 20
Δ = b2-4ac
Δ = 7² - (4 * -6 * 20)
Δ = 49 - (4*-120)
Δ = 49 - (-480)
Δ = 529 Δ > 0
-6x2+7x+20=0
x = -b ∓ √Δ 2a
x' = -7 - √529 2*-6 = -7 - 23.0 -12 = -30.0 -12 = 2.5
x" = -7 + √529 2*-6 = -7 + 23.0 -12 = 16.0 -12 = -1.33333333333
x' = 90.0
x" = -48.0
S = {x ∈ R / x' = 90.0, x" = -48.0 }