Proving "[a]_n ∩ [b]_n is Empty or Equals [b]_n

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SUMMARY

The discussion centers on proving that either the intersection of the sequences [a]_{n} and [b]_{n} is empty or the two sequences are equal. The user attempts to demonstrate that if an element x exists in both sequences, it leads to the conclusion that [a]_{n} must equal [b]_{n}. The proof hinges on the modular relationships defined by x, specifically that if x is congruent to a modulo n and b modulo n, then the difference a-b must equal zero, confirming the equality of the sequences.

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Homework Statement


Prove that either [a]_{n}\cap<b>_{n}</b>=empty set or [a]_{n}=<b>_{n}</b>.

Homework Equations


The Attempt at a Solution


I want to assume there is an element x in [a]_{n}\cap<b>_{n}</b> and show this implies [a]_{n}=<b>_{n}</b>.
This tells me x is in [a]_{n} and <b>_{n}</b>.
That's where I get stuck.
 
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sorry, I meant to show this implies [a]=.
 
If x=a mod n then n|x-a. x=b mod n means n|x-b.

If x|x-a and n|x-b... what can you say about a-b?
 
x-a=x-b
x-x=a-b
0=a-b
b=a
 
x-a is probably not equal to x-b
 
Ok then I'm not really sure where to go with a-b then.
 

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