Hello!
I believe that the repeated formula that is continuing the geometric sequence is "multiply by 2". The rule of the sequence is to multiply by 2 because the first number of the sequence is 5 and when you multiply 5 w/ 2, you get 10. After multiplying 10 w/ 2 as well, you'll get 20, which is the next number in the geometric sequence. Same goes for when you multiply 20 w/ 2. Your result would be 40. So, the recursive formula is to multiply by 2.
I hope this helps!