SOLUTION: Find the greatest common factor and factor it out of the expression. 3x^5y^2-21x^2y^7

Look for a number.

3 is the largest common factor of 3 and 21, so we take out 3

Now look for letters.

x and y appear in both terms, and the LARGEST power we can take
out is the SMALLEST power that appears, which is  and 

So we take out the GCF, which is 



Edwin