1. The problem statement, all variables and given/known data http://postimage.org/] [/PLAIN] [Broken] image url 2. Relevant equations N/A 3. The attempt at a solution I have to solve a different question using a similar method to this one but I cannot figure out how they got the sigma notation into the last equation format. I tried writing out the summation manually as well as the equation substituting n for 0,1,2,3 but they don't match up and I cannot do my next problem without figuring this one out first.