How Can a^r = 1 mod N Be Expressed Differently If a and N Are Coprime?

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The discussion focuses on the mathematical expression of the equation a^r = 1 mod N under the condition that a and N are coprime. It establishes that if a and N are coprime and r is even, the equation can be rewritten as a^(r) - 1 = 0 mod(N). The key takeaway is that the equivalence a = b mod(N) holds if and only if N divides a - b, which is fundamental in modular arithmetic.

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Baggio
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If a and N coprime, a < N and r is even how can

a^(r) = 1 mod(N) be written as


a^(r) - 1 = 0 mod(N) ?

I don't know much number theory (I'm a physics student)

Thanks
 
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Hi, the conditions you list at the start don't matter for what you've just asked (a, N coprime, etc). For any a,b, and N,

a=b mod (N)

if and only if

N divides a-b

if and only if

N divides (a-b)-0

if and only if

a-b=0 mod(N)


Working mod N you can add, subtract and multiply as normal (division isn't always possible!), you just have the luxury of reducing things mod(N) afterwards.
 
ahh i see what you did there.. thanks!
 

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