Given that at n=3: 4 and 4i are zeros:
Then:
[tex]\begin{gathered} (x-4)(x-4i)(x+4i)\Rightarrow(x-4)(x^2-(4i)^2) \\ (x-4)(x-4i)(x+4i)\Rightarrow(x-4)(x^2+16) \\ (x-4)(x-4i)(x+4i)\Rightarrow x^3+16x-4x^2-64 \\ (x-4)(x-4i)(x+4i)\Rightarrow x^3-4x^2+16x-64 \end{gathered}[/tex]Hence the function is:
[tex]F=x^3-4x^2+16x-64[/tex]