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## Trouble Proving Cyclotomic Polynomial Identity

We are required to show that $$x^n-1=\prod_{d|n}\phi_{d}(x)$$ I am aware this is considered a trivial identity and that there are numerous ways to prove it, however, I am having trouble understanding this specific argument used by the author. I am particularily confused as to how he was motivated in defining various variables such as d […]