(x-y)^2 (x+y)^2 (x^2+y^2)^2
= [(x-y) (x+y)]^2 (x^2+y^2)^2
= (x^2-y^2)^2(x^2+y^2)^2
= [(x^2-y^2)(x^2+y^2)]^2
= (x^4-y^4)^2
= x^8 - 2x^4y^4 + y^8
(x-y)^2 (x+y)^2 (x^2+y^2)^2
= [(x-y) (x+y)]^2 (x^2+y^2)^2
= (x^2-y^2)^2(x^2+y^2)^2
= [(x^2-y^2)(x^2+y^2)]^2
= (x^4-y^4)^2
= x^8 - 2x^4y^4 + y^8