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 P: 688 Given that $$a^{p-1} = a^{ke+r} \equiv a^e \equiv 1 \pmod p$$ you are to prove that r=0. Consider that $$a^{ke+r} = a^{ke} a^r = (a^{e})^k a^r$$ (now, doing some more work, where can you get at?) and remember that r