-6x2 +21x -15 = 0
ax2 bx c = 0
a = -6
b = 21
c = -15
Δ = b2-4ac
Δ = 21² - (4 * -6 * -15)
Δ = 441 - (4*90)
Δ = 441 - (360)
Δ = 81 Δ > 0
-6x2+21x-15=0
x = -b ∓ √Δ 2a
x' = -21 - √81 2*-6 = -21 - 9.0 -12 = -30.0 -12 = 2.5
x" = -21 + √81 2*-6 = -21 + 9.0 -12 = -12.0 -12 = 1.0
x' = 90.0
x" = 36.0
S = {x ∈ R / x' = 90.0, x" = 36.0 }