What are potential roots of p (x) = x4 - 9x2 - 4x + 12

Hello:

x4 - 9x2 - 4x + 12 = x² (x²-9) - 4 (x-3)

=x² (x-3) (x+3) - 4 (x-3)

= (x-3) (x² (x+3) - 4)

= (x-3) (x3+3x²-4)

= (x-3) (x-1) (x²+4x+4)

x4 - 9x2 - 4x + 12 = (x-3) (x-1) (x+2) ²

potential roots is : 3; 1 : - 2