
Arturo O. answered 11/07/17
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Assuming the polynomial has real coefficients, the complex conjugate of a complex zero must also be a zero. So far the zeros are
1
-4
-3i
3i
If the polynomial is of degree 4,
P(x) = A(x - 1)(x + 4)(x + 3i)(x - 3i)
A ≠ 0
Note that (x + 3i)(x - 3i) = x2 + 9
P(x) = A(x - 1)(x + 4)(x2 + 9)
You can expand this into standard form if you wish. Note that all of the coefficients are real, even though there are two complex zeros.