Hi, I'm currently trying to do some modular arithmetic questions but I don't really know where to start, I don't have much in the way of examples, only a list of theorems. I'm no genius so theorem's by themselves are not enough to enable me to apply them so I've been stuck on some questions. Can someone help me with them?(adsbygoogle = window.adsbygoogle || []).push({});

Q1. Find an [tex]r \in Z[/tex] such that [tex]0 \le r < 713[/tex] and [tex]48^{307} \equiv r\left( {\bmod 713} \right)[/tex]. A possible answer is 12.

The next question is similar I think but I haven't been able to figure out what to do.

Q2. Find an m where 0 <= m < n and [tex]m \equiv l\left( {\bmod n} \right)[/tex] with l = 482 and n = 14.

I don't necessarily expect anyone to do the whole pronblem for me, even an indication as to the required technique would be good. This is because I really have no idea as to how to approach the first two.

I just have one more question that I would like someone to respond to. I have the following theorem:

Let m and n be in the set of integers Z with m,n > 1. Then, [tex]\mathop n\limits^\_ \in Z[/tex] has a multiplicative inverse if and only if gcd(m,n) = 1.

Note: The second sentence has n bar, it's probably a little hard to see. The first sentence in the theorem has n just being n, not n bar.

The following question is from my question booklet and I'm wondering if the theorem applies to it in some way. My understanding of n bar is that it is the set of integers z such that [tex]z \equiv n\left( {\bmod m} \right)[/tex]. But when I say 'my understanding' I only mean that I know the definition. I'm not really sure at all as to what this means in practice, I'm lacking in suitable examples to work with so any help with the questions would be really good thanks.

Q. Find an inverse for 41 modulo 660, and use it to find the least positive integer x satisfying: [tex]41x \equiv 125\left( {\bmod 660} \right)[/tex]

Edit: Just one more thing. I have that z_m(z subscript m) denotes the set of all congruence classes modulo m. Does that mean if for example m = 3 then z_m would denote [tex]\mathop a\limits^\_ = \left\{ {z \in Z|z \equiv a\left( {\bmod 3} \right)} \right\}[/tex] or something like that?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Modular arithmetic questions

**Physics Forums | Science Articles, Homework Help, Discussion**