Recommended

But what is a Fourier series? From heat flow to drawing with circles | DE4

Why people recommend it

3Blue1Brown's animated explanation of Fourier series, linked by electrical engineers as an intuitive grounding before tackling Fourier and Laplace transforms.

Watch for: Maths-focused rather than circuit-focused; best alongside his Fourier transform video

In their words

The mathematics behind this is exquisite, and I strongly recommend that you watch the videos by Khan Academy and 3Blue1Brown on this and related topics.
Simon Fitch on electronics.stackexchange.com, Oct 2021. CC BY-SA.

Then go look at what is a Fourier series?.
jonk on electronics.stackexchange.com, Nov 2019. CC BY-SA.

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