I would second the recommendation for Who is Fourier? A Mathematical Adventure. It's an unusual and engaging introduction to waves, Fourier coefficients, and tr

I would second the recommendation for Who is Fourier? A Mathematical Adventure. It's an unusual and engaging introduction to waves, Fourier coefficients, and transforms. The slope is gentle but not dumbed down. https://www.amazon.com/Who-Fourier-Mathematical-Adventure-2nd/dp/0964350432#:~:text=In%20Who%20is%20Fourier%3F,exponentiation%2C%20differentiation%2C%20and%20integration https://www.amazon.com/Who-Fourier-Mathematical-Adventure-2n....