Hello,

- if x = -3 is a solution then the corresponding linear factor is (x+3)

- if x = 4i is a solution then x = -4i is a solution too. Otherwise you will get an equation containing imaginary numbers. The linear factors are now (x-4i) and (x+4i).

- f(x) = (x+3)(x-4i)(x+4i) = (x+3)(x^2+16)