http://i34.tinypic.com/23r747b.jpg

I think I get the setup, but I'm having trouble simplifying it. It's getting so long with the cube factored out ...is there an easier way?

I have: E (as in sigma) [2(-5+3i/n)^3(3/n)]

I simplified it further by factoring out the cube but it seems like it's way too complicated now. Any ideas how to avoid this, or am I way off?

Thanks :]