Hi there,

I have a trigonometrical-series type of solution as follows:

I am having trouble calculating the sum part of the expression. Let's assume

and x = 0 and divide through by , then I get the sum part to be:

The reference I am using gives the overall answer to be:

but I am gettingmuchsmaller answers. Could anyone suggest what I might be doing wrong?

Any help would be much appreciated