f(x)
[tex]f(x) = 3 + 24 - 3x {?}^{2} { - x}^{3} [/tex]

f ' (x) = 24 - 6x - 3x^2

-3x^2-6x + 24 =0

3x^2 + 6x - 24=0

x^2 + 2x - 8 = 0

D = 6

x= - 2 +/- 6/2

x1= 2     x2= -4