1. The problem statement, all variables and given/known data I'm trying to solve this DE: 4xy''+2y'+(cosx)y=0 using a series solution. 2. Relevant equations 3. The attempt at a solution See attached PDF. I tried writing the cosine term as an infinite series, but that gives me a messy double summation. And in the end, I get an index that is not an integer... Any hints on how to deal with the cosine term?