-15x2 +21x -6 = 0
ax2 bx c = 0
a = -15
b = 21
c = -6
Δ = b2-4ac
Δ = 21² - (4 * -15 * -6)
Δ = 441 - (4*90)
Δ = 441 - (360)
Δ = 81 Δ > 0
-15x2+21x-6=0
x = -b ∓ √Δ 2a
x' = -21 - √81 2*-15 = -21 - 9.0 -30 = -30.0 -30 = 1.0
x" = -21 + √81 2*-15 = -21 + 9.0 -30 = -12.0 -30 = 0.4
x' = 225.0
x" = 90.0
S = {x ∈ R / x' = 225.0, x" = 90.0 }