The expresssion x4+4 can be factorized as
(x2+2x+2)(x2−2x+2)
(x2+2x+2)(x2+2x−2)
(x2−2x−2)(x2−2x+2)
(x2+2)(x2−2)
x4+4=x4+4+4x2−4x2=(x2)2+(2)2+2×x2×2−(2x)2=(x2+2)2−(2x)2(x2+2+2x)(x2+2−2x)=(x2+2x+2)(x2−2x+2)