Method 1:
\Factor the each monomial.
\3x = 3 · x
\7xy2 = 7 · x · y · y
\The GCF is the product of the common prime factors in each monomial.
\GCF = x
\The greatest common factor of 3x and 7xy2 is x.
The greatest common factor of 3x and 7xy2 is x.