The greatest common factor, or GCF, is the greatest factor that divides two numbers. To find the GCF of two expression
1. List the prime factors of each number.
2. Multiply those factors both numbers have in common. If there are no common prime factors, the GCF is 1.
16x^4y^3 = ( 4*4)(x*x*x*x)(y*y*y)
12x^2y^7 = (4*3)(x*x)(y*y*y*y*y*y*y)
So common to them is 4x^2y^3