8a^3 b^2 = 2*2*2 *a*a*a *b*b
12ab^4 = 2*2*3 *a*b*b*b*b
to find the CGF, multiply those factors both numbers have in common
GCF: 2*2 *a*b*b
CGF 4*a*b^2
4ab^2
