I'm slightly confused about something in a question on a past exam paper for my Fourier analysis module.

I have a question were f(x) is sinx on the interval [0, pi], and f bar denotes the periodic extension with period pi of f.

It asks me to sketch the graph of f bar, and show on the interval [-pi, pi] that f bar is even. I can do both of these. It then asks me to calculate the trigonometric Fourier series of f. I'm just not sure which interval it wants me to use, that with the extention or without. Also, can I ignore the an cosnx part of the Fourier Series formula as I know I am calculating for sinnx? The first couple of lines of the calculation would be appreciated.