Decomposing signals into frequencies: Fourier series and convergence (Dirichlet, Fejér, Gibbs), the Fourier transform and Plancherel, convolution, the FFT, the uncertainty principle, wavelets, the Dirac delta and distributions, and harmonic analysis on groups.
Free to start · adaptive placement finds your level · reviews timed to your own forgetting.
Every idea is taught with motivation and a worked example before the drills, and an FSRS spaced-repetition engine schedules each review for the day its model predicts you would forget it. A short placement check finds what you already know, so you start Fourier & Harmonic Analysis exactly where it's useful.