In this blog entry you can find lecture notes for Math2111, several variable calculus. See also the table of contents for this course. This blog entry printed to pdf is available here.

We motivate the formulae for Fourier series. For simplicity we ignore here all questions concerning convergence, which are dealt with in Section 3 and the additional material.

**Fourier series**

As pointed out in the post on Section 2 at the beginning, in order to represent a function we need an orthonormal bases with respect to the inner product