Hi there. I have to find the Fourier development for

So this is what I did, I think its wrong, but I don't know where I did the mistake.

Then:

When I plot this on mathematica I get a line. So, I think I've made a mistake somewhere, but I don't know where the error is. Somehow I have to define the zero intervals, I think I should use the heaviside function.

Bye and thanks for 'ur help.

PS:I didn't know where to post this, so move it if it should be in another subforum.