Simplify and Write Without Negative Exponents $\left(x^{a}-n-y^{a+n}\right)\left(x^{a+n}-2 y^{a-n}\right)$

Simplify and write without negative exponents: $\left(x^{a}-n-y^{a+n}\right)\left(x^{a+n}-2 y^{a-n}\right)$