Linear equations can either have a single solution, infinite solutions, or no solutions. Learn how to determine the number of solutions to a given equation, and how to create equations with a desired number of solutions.
Some of Sal's oldest (and roughest) videos on algebra. Great tutorial if you want to see what Khan Academy was like around 2006. You might also like it if you feel like Sal has lost his magic now that he doesn't use the cheapest possible equipment to make the videos.