In my Discrete Mathematics class we are are covering divisibility. One of the problems that the professor covered (quite terribly) is the following: 1. The problem statement, all variables and given/known data Prove or salvage: If a|bc, then a|b. 2. Relevant equations Relevant concepts: Relatively prime numbers Divisibility 3. The attempt at a solution I know that the statement is wrong as it is. I also know that in order to salvage the statement, I must say that a and c are relatively prime. The problem is that I do not know how to rigorously prove this. Could somebody guide me in how to do this. Teach a man to fish!