Abstraction, the fundamental idea of algebra

Using letters to denote numbers may look like just a simple trick of notation, but it is the fundamental idea of algebra. Abstraction allows us to do general computations, not just arithmetic calculations with actual quantities. Here is a handout for the first class of an Algebra/Pre-Calculus class. This also shows that if someone is able to solve an equation (no matter how simple), then he/she has already obtained the key skill needed for computer programming.