x4y4 + 4
= x4y4 + 4x2y2 + 4 - 4x2y2
= (x2y2 + 2)2 - (2xy)2
= (x2y2 - 2xy + 2)(x2y2 + 2xy + 2)
x4y4 + 64
= x4y4 + 16x2y2 + 64 - 16x2y2
= (x2y2 + 8)2 - (4xy)2
= (x2y2 - 4xy + 8)(x2y2 + 4xy + 8)
x5 + x + 1
= x5 - x2 + x2 + x + 1
= x2(x3 - 1) + (x2 + x + 1)
= x2(x - 1)(x2 + x + 1) + (x2 + x + 1)
= (x2 + x + 1)[x2(x - 1) + 1]