
James L. answered 03/21/20
Tutoring for AP and IB Physics and SAT Math
Well start with left side of (x + 8 )(x - 8)(x + i)(x - i) and set equal to zero. Note that there are four values that make the left side zero, among them 8 and i.
Multiply out the left side and you get (x^2 - 64)(x^2 + 1) = x^4 - 63x^2 - 64 = 0, which has a coefficient of 1 on x ^4 term as required.