# Help: finding materials to study coprime numbers

Hello, everybody.

My teacher recently (a year ago) gave me some sheets with problems about coprime numbers, however, without help I couldn't solve even one problem. It is quite sad because I usually don't feel so beat down by math that I wouldn't even get an idea of where to start with solving a problem. That got me thinking that perhaps I lack understanding of coprimes. Perhaps anyone know great resources for learning some stuff about them? Keep in mind that I am not really advanced in math and that all things about coprimes that I know are that greatest common divisor of all the coprime numbers are 1 (recently got into phi function as well, but that is not helping me at all in doing those problems :( ).

Examples of problems that I am struggling with:

1: Prove that if $a$ and $b$ are coprime, then $a^m$ and $b^m$ are also coprime, if $m$ is any natural number.

2: Prove that if $a$ is a prime number, which isn't equal to 2 nor 3, then $a^2 - 1$ is a multiple of 24. (Oh, I think that I lack of understanding of prime numbers as well)

And quite a lot more. (I understand when someone give the solution to problem, but I can't grasp any of them on my own...)

If you don't know any books, but can give me some advice, I would be glad to read it :)

Note by Zyberg Nee
3 years, 5 months ago

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First example: As $\gcd(a,b)=1$, a and b have no common prime factors. They won't have any common prime factors when they are raised to a natural number. The result follows.

Second example: All prime numbers>3 are of the form $6n \pm 1$ where n is a positive integer.

So, $a^2-1=36n^2 \pm 12n=12n(3n \pm 1)$.

If n is even, 24 all divide 12n and if n is odd, 24 will divide $12(3n \pm1)$.

Proved.

- 3 years, 5 months ago

Check out greatest common divisor and euclidean algorithm.

Staff - 3 years, 5 months ago

Thank you very much!

- 3 years, 5 months ago