Tuesday, 11 April 2017

elementary number theory - Prove that for every pair of coprime positive integers p,q, (xpq1)(x1) is divisible by (xp1)(xq1).





Prove that for every pair of coprime positive integers p,q the expression (xpq1)(x1) is divisible by (xp1)(xq1).




My attempts:



xpq1=(xp)q1 which is divisible by xp1



again, xpq1=(xq)p1 which is divisible by xq1.




But how to prove that it is divisible by their products?
Just now an idea struck me. Can I consider gcd of xp1 and xq1 as x1 ?. If yes, then we are done!


Answer



To answer your question, if the exponents are not coprime, you can try to prove the general formula:
gcd
from which you can deduce that \;(x^{mn}-1)(x^{\gcd(m,n)}-1) is divisible by \;(x^m-1)(x^n-1).


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