factor until nothing else can be factored
factoring numbers into primes
if there are exponents on a factor, rewrite them without an exponent
42x3y 2*3*7*x*x*x*y
70xy2 2 *7*x *y*y*5
2 7 x y
The greatest common factor is the product of the shared factors
=2*7*x*y
=14xy