• Review of Ordinary Differential Equations (ODEs) (PDF)
• Review of 1st-order Partial Differential Equations (PDEs) (PDF)
• Review of Fourier Transforms (PDF)
• Review of Lectures 20 and 21 on Wave Dispersion (PDF)
• Review Session on Homework 2 (PDF)

Here is an interesting article called "Can you hear the shape of a drum?"