Could someone please give me some advice on solving these problems(adsbygoogle = window.adsbygoogle || []).push({});

1. find the last digit of the decimal expansion 7^999999?

I think i have to do something like 7^999999(mod10) but i'm not really sure if that's right or how i would do that

2. Show that every positive integer relatively prime to 10 divides infinitely many repunits? I don't know what a repunit is or how i would even begin this problem.

Thanks

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# Homework Help: Number theory help

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