trigonometric summation in maxima



Hi all
   I am interested in evaluating summation involving trigonometric terms 
using maxima. For example

sum(cos(j/N), j, 1, N)

Maxima does not give the simplified answer but gives expression 
involving summation sign. How to get the simplified result?

I read the manual and came across simpsum : true flag. But this does not 
simplify the above expression. simpsum : true works only for Riemann 
kind of sums.

Any ideas how to extend the sum function to trignometric terms also?

thanks
raju

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