Hello I have the following proposition to prove. Prop. Let a,b be integers. If 1 is a linear combination of a and b, then a and b are relatively prime. I am given the following definition. Let a and b be integers, not both zero. If gcd(a,b)=1, then a and b are said to be relatively prime. Notice that the only common divisors of relatively prime integers are 1 and -1. My work so far: (1) Let a,b be integers. (2) By definition of linear combination there exist integers x,y such that 1=ax+by. (3) Because 1 is a common divisor of a,b then 1 must be the gcd(a,b) (4)Therefore a and b are relatively prime I need help on (3), I know that I am missing some steps and logic but I am not sure what to do. Am I approaching this correctly? Thank you.