\[x^{6} - y^{6} = \left( x^{2} - y^{2} \right)\left( x^{4} + x^{2}y^{2} + y^{4} \right) =\]
\[= (x - y)(x + y)\left( x^{4} + x^{2}y^{2} + y^{4} \right).\]