Alinssexislogach Alinssexislogach 21-11-2016 Mathematics contestada Understanding this proof for the proposition "For all integers a, gcd(9a+4, 2a+1) = 1. Proof: gcd(9a+4, 2a+1) = gcd(2a+1, a) = gcd(a, 1). Since gcd(a, 1)=1, gcd(9a+4, 2a+1) =1.