Friday, 6 July 2018

elementary number theory - Congruence proof using gcd concepts



Anyone can help me? The problem is:



We have that $a \equiv b (\mod p)$, $x|a, x|b$, and $x$ and $p$ are relative primes, $\gcd(x,p)=1$. How to show that $\dfrac{a}{x} \equiv\dfrac{b}{x} (\mod p)$?



Thanks in advance.


Answer




Hint $\ $ By Euclid's Lemma, $\rm\, gcd(x,p)=1,\ \ x\mid \color{#c00}{a\!-\!b = pn}\:\Rightarrow\:x\mid n.\ $ Cancel $\rm\,x\,$ from $\rm\color{#c00}{a,b,n\ there}$.


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