Givem that at n = 3: 4 and 4i are zero;
Then;
[tex](x - 4)(x - 4i)(x + 4i) \: (x - 4)( {x}^{2} - ( {4i)}^{2} \\ (x - 4)(x - 4i)(x + 4i) \: (x - 4)( {x}^{2} + 16) \\ (x - 4)(x - 4i)(x + 4i) \: {x}^{3} + 16x - {4x}^{2} - 64 \\ (x - 4)(x - 4i)(x + 4i) \: {x}^{3} - {4x}^{2} + 16x - 64[/tex]
Hence the function is:
[tex]f = {x}^{3} - {4x}^{2} + 16x - 64[/tex]