-3x2 +18x +21 = 0
ax2 bx c = 0
a = -3
b = 18
c = 21
Δ = b2-4ac
Δ = 18² - (4 * -3 * 21)
Δ = 324 - (4*-63)
Δ = 324 - (-252)
Δ = 576 Δ > 0
-3x2+18x+21=0
x = -b ∓ √Δ 2a
x' = -18 - √576 2*-3 = -18 - 24.0 -6 = -42.0 -6 = 7.0
x" = -18 + √576 2*-3 = -18 + 24.0 -6 = 6.0 -6 = -1.0
x' = 63.0
x" = -9.0
S = {x ∈ R / x' = 63.0, x" = -9.0 }