(x^10+y^10)(x^2+y^2)-(x^8+y^8)(x^4+y^4)
=x^12+x^10y^2+y^10x^2+y^12-x^12-x^8y^4-x^4y^8-y^12
=x^10y^2+y^10x^2-x^8y^4-x^4y^8
=x^2y^2(x^8+y^8-x^6y^2-x^2y^6)
=x^2y^2[x^6(x^2-y^2)+y^6(y^2-x^2)]
=x^2y^2[x^6(x-y)(x+y)-y^6(x-y)(x+y)]
=x^2y^2(x^6-y^6)(x-y)(x+y)
=x^2y^2(x-y)(x+y)(x^2+xy+y^2)(x^2-xy+y^2)(x-y)(x+y)
=x^2y^2(x-y)^2(x+y)^2(x^2+xy+y^2)(x^2-xy+y^2)