(x2n+xnyn+y2n)(xn-yn)(x3n+y3n)
\(=\text{[}\left(x^n\right)^2+x^ny^n+\left(y^n\right)^2\text{]}\left(x^n-y^n\right)\left(x^{3n}+y^{3n}\right)\)
\(=\left[\left(x^n\right)^3-\left(y^n\right)^3\right]\left(x^{3n}+y^{3n}\right)\)
\(=\left[x^{3n}-y^{3n}\right]\left(x^{3n}+y^{3n}\right)\)
\(=\left(x^{3n}\right)^2-\left(y^{3n}\right)^2\)
\(=x^{6n}-y^{6n}\)