First determine the greatest common numerical factor of each coefficient. You can use prime factorization or the list method to find the greatest common numerical factor. The numerical factors are -49 and -343. Because -1 is a common factor of each coefficient, find the GCF of 49 and 343. Factors of 49:1, 7, 49 Factors of 343: 1, 7, 49, 343 What is the GCF of 49 and 343? Multiplying the GCF of 49 and 343 by -1 gives the GCF of -49 and -343. What is the GCF of -49 and -343?