How Do You Compute the DFT of Periodic Signals?

[ankh]

Homework Statement

Find the discrete Fourier transform X[k] = DFTn {x[n]} of the following
periodic sequences x[n] = x[n - N] with period N:

(a) For n = 0 . . .N - 1 we have x[n] =\delta[n].
(b) For n = 0 . . .N - 1 we have x[n] = \mu[n] -\mu[n - K] with K < N.
(c) x[n] = cos( (2*pi*M*n)/N ).

Homework Equations

We don't have a book for my digital processing class and i missed couple of classes so i have no idea how to start these problems. A little hint or a link to a good tutorial/source would be greatly appreciated.

The Attempt at a Solution

 

[Redbelly98]

Wikipedia has good info:

http://en.wikipedia.org/wiki/Discrete_Fourier_transform#Definition