may i know when do you use fourier series and when do you use half range expansion ( fourier sine/ cosine)? i cant seem to be able to figure out what is the differences apart from that one has only either cos or sine.
Easy: If the function is even then a cosine series will do, and if it is odd a sine series will do. This is just to say that for an even function all sine coefficients will be zero, and for an odd function all cosine coefficients will be zero.