-12x2 +9x +21 = 0
ax2 bx c = 0
a = -12
b = 9
c = 21
Δ = b2-4ac
Δ = 9² - (4 * -12 * 21)
Δ = 81 - (4*-252)
Δ = 81 - (-1008)
Δ = 1089 Δ > 0
-12x2+9x+21=0
x = -b ∓ √Δ 2a
x' = -9 - √1089 2*-12 = -9 - 33.0 -24 = -42.0 -24 = 1.75
x" = -9 + √1089 2*-12 = -9 + 33.0 -24 = 24.0 -24 = -1.0
x' = 252.0
x" = -144.0
S = {x ∈ R / x' = 252.0, x" = -144.0 }