Step-by-step explanation: Let's begin by finding the
greatest common factor for the numbers 65 and 39.
I would make a factor tree and break up 65 and 39.
So 65 is 13 x 5 and 39 is 13 x 3.
Since the 13's match up, the greatest
common factor between 65 and 39 is 13.
For the variables, we use the smallest power on each of them.
So we use a^3 and b^4 to get 13a^3b^4 as our GCF.