Skip to content
Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

partial-differential-equations

Choosing which series a boundary-condition pair calls for

taught

Match a stated pair of boundary conditions -- Dirichlet, Neumann, Robin, mixed -- to the sine, cosine, full, or transcendental eigenfunction series it forces, before attempting to solve.