Question: what is the greatest common factor of 45 and 63 using prime factorization?
Answer: The prime factorization of 63 is: 3 x 3 x 7. The prime factors and multiplicities 45 and 63 have in common are: 3 x 3. 3 x 3 is the gcf of 45 and 63. gcf(45,63) = 9.