1. The problem statement, all variables and given/known data Find the Summation Notation and Radius of Convergence of this series. 5, x, 10, x, .... 3. The attempt at a solution I don't know how did they come up with that equation.. But the summation seems right.. Can anyone tell me how did they arrive with that equation? I've tried using the common ratio but I don't know what to do after having the ratio.. And for the radius of convergence, its L = lim (An+1)/(An) as n=> infinity.. Using the summation notation, I ended up infinityinfinity over infinityinfinity. I thought its equal to 1.. ~_~ Sorry, seems like the latex codes now isn't the same as the latex codes before. I don't know how to use the new latex codes..