I'm trying to do some extra course work to prepare for my final next week but I'm having a lot of trouble with the book problems. They talk about a lot of things we weren't taught. Can someone help me out here? Prove: n[itex]\ni[/itex]Z, n= a multiple of gcd(a,b) ⇔ n is a linear combination of a and b This question makes no sense to me. How do I prove that and where can I start. What does gcd have to do with linear combinations.