What are the real or imaginary solutions of the polynomial equation x^4-52x^2+576=0?

rewriting x^4 as A^2 and x^2 and A.

A^2-52A+576=0
(A-36)(A-16)=0
A=36,16

since A is x^2,

x^2=36 and x^2=16
x=6 and -6 and x=4 and -4