Find all complex zeros for the following polynomial function. Please show all of your work.

Question

f(x) = x^4 - 91x^2 - 900

Hi, I need help... I'm not understanding this complex zero..

Answer 1

Substitute: x^2=z => x^4=z^2

z^2-91z-900=0
(z-100)(z+9)=0
If z=100, x^2=100 then x=10 or x=-10
If z=-9, x^2=-9=9i^2 then x=3i or x=-3i