I am studying Real analysis , and there is a question that I am not sure if I should ask it under Number Theory section but I will ask it anyway

Does anyone know how to prove this?

a^{n}- b^{n}= (a-b) (a^{n-1}+ a^{n-2}b +....... + ab^{n-2}+ b^{n-1})

Does anyone know how to prove this or know at least to which category does this kind of question goes to so I can ask to the right place? Thank you.