Saturday, 5 September 2015

Elementary number theory proof involving multiplied gcd's

I'm having trouble proving the following if and only if statement:



For all integers $a,b,n$, prove that $n|gcd(a,n)gcd(b,n)$ if and only if $n|ab$




For proving $n|gcd(a,n)gcd(b,n)\implies n|ab$, I tried using Bezout's Lemma for both $gcd$s and expanding but didn't know how to show that $n$ divided $ab$.



Also didn't didn't how to approach the converse. Any help?

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