Right I'm currently revising this stuff too so ill give it a go...

Is it supposed to be expressed in real form or complex?

Heres the complex form:

And heres the real form:

Heres what it all means...

BUT... This is for when the function is periodic... But yours is periodic (i.e. . So you must change the integral limit accordingly.

If the function is odd the a_k = 0 and if its is even then b_k = 0. So as the sine function is odd... a_k = 0!

Is this enough to start you off?