Hello everyone

I am considering the following equation:

Which looks like this:

And need to expand it in terms of a Fourier series. I know the above function is continuous, differentiable and -periodic, hence there should exist a convergent Fourier series of the form:

With coefficients given as:

However I get, in both cases, and . The only thing I find to be non-zero is .

Can anybody help me realizing where I am going wrong?

Kind Regards