Proving gcd(a,n)=(a-1,n)=1 and its implications on mod calculations

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In summary, In order to prove that if gcd(a,n)=(a-1,n)=1, then 1+a+...+a^0 mod n, a student would need to know what gcd is, how to calculate it, and understand that if a and n are relatively prime then the result is 1. Additionally, the student would need to know how to show that if m and k are positive integers then (^k)=m^k-1(m). Lastly, the student would need to be able to show that if a==0 mod b and b==0 mod a then => ab==0 mod(ab).
  • #1
1+1=1
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i just can't finish up these proofs but i have my ideas written down on the bottom. also, i have what i think is right written down, but it IS A LOT of stuff to type. can anyone point me in the correct direction to go?

i need to show that if gcd(a,n)=(a-1,n)=1, then 1+a+...+a^0 mod n

show (m,n)=1 then m 1 mod (mn)

show if m and k are positive integers then (^k)=m^k-1(m)

what i know so far: the second one can use fermat's little theroem correct? if a==0 mod b and b==0 mod a then => ab==0 mod(ab)

the third one is just playing with my brain, i honestly do not know anywhere to start it.

the first question says what a,n are relatively prime, and a-1,n are also relatively prime. so, if any a raised to a power, that a is == to 0, mod n. can anyone give me a "hint"?

thank you! p.s. does my LaTeX look good? feel free to tell me and all. :redface: :smile:
 
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  • #2
1+1=1 said:
i just can't finish up these proofs but i have my ideas written down on the bottom. also, i have what i think is right written down, but it IS A LOT of stuff to type. can anyone point me in the correct direction to go?

i need to show that if gcd(a,n)=(a-1,n)=1, then 1+a+...+a^0 mod n
What? Your consequent is "1 + a + ... + a^0 mod n." I don't see how that can even be assigned a truth value. Wouldn't a^0 just be 1 (assuming we're talking about natural numbers for a).

show (m,n)=1 then m 1 mod (mn)
Again, the consequent is "m 1 mod (mn)." Is this supposed to make sense. Perhaps it's some notation I've never seen, as I've really dealt much at all with number theory.

show if m and k are positive integers then (^k)=m^k-1(m)
What is (^k)? And isn't 1(m) simply m?

thank you! p.s. does my LaTeX look good? feel free to tell me and all. :redface: :smile:
You didn't use any LaTeX (although you probably should have)!
 
  • #3
1+1=1,

I strongly suggest you re-write your questions more carefully. It's too much effort for us to have to decipher what you mean. Try to spend some time phrasing your queries in a manner that would be easy for others to comprehend. It's not fair that we have to spend a whole bunch of time guessing your intent.
 
  • #4
At the risk of sounding pissy again, when you say: I can use Fermat's little theorem, right, (paraphrasing) it demonstrates you've not actually attempted the question. This does not make you stuck, seeing as you've not started it. You don't just read a maths question and see the answer anymore, you have to do some work and think it through. When you become a maths teacher, how would you respond to a kid who when asked why they couldn't do a question said something like 'cos I've not tried to do it'?
 
  • #5
as i say to everyone, i intend to teach useful mathematics, not abstract. my intentions are to teach algebra, geometry, trig., etc. the usefulness of this number theory to me is tasteless in my classroom and i am only in this class becuase of requirements. do you honestly think that students in the high schools actually understand congruences and modulos? i know of some that cannot even understand basic mathematical concepts, i.e. addiing, subtracting, multi, and division.

again, i wonder to myself i know that i may not be the best descriptive person on my math problems, but still that does not mean i get a verbal bashing everytime i make a type-o. look at others' posts, critique them too. i only ask for a little help, and i get haggled...
 
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  • #6
oh, cos no one's ever found a use for number theory and congruences, right...

but that still doesn't affect the idea that you might meet some students who have exactly the same attitude towards what you consider useful mathematics, and they don't?

sorry it's to your distaste to have to learn the subject that enables you to, say, buy books from amazon online and not have your credit card ripped off, but irrespective of what the subject is you don't appear to be even trying to understand how to do the questions, and if you can't be bothered to learn it (and these questions are both simple and elegant) why should we be bothered to explain it?
 

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