Method 1: By Listing FactorsList out all factors of each number, and find the first common one.Factors of 36 : 1, 2, 3, 4, 6, 9, 12, 18, 36
Factors of 39 : 1, 3, 13, 39
Therefore, the GCF is 3.
List all prime factors of each denominator, and find the intersection of these primes.Prime Factors of 36 : 2, 2, 3, 3
Prime Factors of 39 : 3, 13
Therefore, the GCF is 3.