First Order Differential Equations
Jeremy Orloff, a lecturer in the math department, has provided a brief review of how to solve first order differential equations. Link
Second Order Differential Equations
Khan Academy's explanation of second order differential equations is quite good. Note that it is in a sequence, just like MITx's videos are. Here is the link.
Jeremy Orloff has also provided a relatively detailed review of complex numbers. Link
Non-rigorous treatments for first and second order equations
- See wiki on first order circuits for a treatment of first order systems, and
- wiki on second order circuits for second order systems.
For a different approach to both first and second order differential equations (just a brief review, no rigor), also see this wiki article