Question 971182
One of your zeros is complex with an imaginary component.  Complex zeros of polynomial functions
occur as conjugate pairs.  Your THREE zeros are 7, 5i, and -5i.


The factored form of the polynomial with those roots is  {{{(x-7)(x-(5i))(x-(-5i))}}}.  You know of course about {{{i^2=-1}}}.


Take this the rest of the way.