I've done a power series solution to a differential equation and got the recursive formula for the coefficients below. Now I am to evaluate it for large j and I don't get the answer in the book.
I'm not sure what method they are using to get the answer although their answer makes sense physically.
a j+1 = aj * 2 * {(j + L + 1)  k }/ ( {j+1}(j + 2L + 2) )
where L and k are constants and j is just an integer index number.
If I consider large j I would say
aj+1 approx. aj * 2 (j) / ( j * j) = aj * 2/j
If I say j => infinity and use l'Hopital's rule I get
aj+1 = aj * 2 / (2j + 2L + 3) approx. aj * 1/j
The book gets
aj+1 approx. aj * 2j / ( j*(j+1))
What rules are they applying to get this?
(of course a j+1 means a_{j+1} and aj means a_{j} )
