G285 2021 Fall Problem Set Problem 8
Problem
Find
Solution
We begin with a simpler problem . Now, suppose and are constant. We have a converging geometric series for with a sum of . Now, make everchanging. We have , so the entire sum must be .
Now, coming back to the original problem, we split the single sum into : Split into single variables to get Now, generalize to obtain . Using the geometric series formula we have Now, we can plug this in for all to get