1. The problem statement, all variables and given/known data Investigate the convergence of the following series. (2n)!/(n!n!) 3. The attempt at a solution Number one, I don't see how they get that if an = (2n)!, then an+1 = ((2n+2))!, it should be (2n+1)! Number two, I don't see how they go to the second step, why is the second step not: (n!n!(2n+2)!)/((n+1)!(n+1)!(2n)!)? why do they have that extra (2n)! in the numerator? Number three, I don't see why n!n! cancels in the numerator in step 3.