$$(x^{2}+y^{2})(x^{2}+xy+y^{2})$$
$x^{4}+xy^{3}+y^{4}+yx^{3}+2\left(xy\right)^{2}$
$\left(x^{2}+y^{2}\right)\left(x^{2}+xy+y^{2}\right)$
