Question

If 9i is a root of the polynomial function f(x), which of the following must also be a root of f(x)?

A.-9iB.-1/9i C.1/9i D.9-i

Answer 1

Hello,

conjugate of 9i is -9i is also a root.
Answer A

Answer 2

If you have a complex root of a polynomial function a+bi it must have also it's conjugate a-bi as a root.
If 9i is a root for polynomial function f(x) then also is -9i.

Final answer: A. -9i