In order to find the greatest common factor of two monimial, we must find the prime factorization of each monomial, including all the variables.
For instance,
[tex]40x^5=1\cdot4\cdot10x^3x^2[/tex]and
[tex]70x^3=1\cdot7\cdot10x^3[/tex]By comparing both results, we can see that the greastest common factor is
[tex]10x^3[/tex]