Factoring is the opposite of expanding. It is a useful technique for finding the roots of equaions. There are several things to look for when factoring. the first is to look for common factors. Watch this example to learn how to spot and deal with common factors:

Just as FOIL can be used to expand, so we can return an equation to factored form using a similar idea. Watch this example for a quick review on how FOIL-ing works, and how we can go backwards to wite a quadratic equation in factored form:

We can use the idea of un-FOIL-ing to tackle more complicated examples, too. The following example will show you how to deal with quadratic equations involving common factors and negative coefficients: