At a Glance - FOIL
Officially, we use the FOIL method to multiply binomials. If you need a quick refresher (or introduction) to binomials, those are expressions that consist of two terms—you know, as in "a + b" or "Mike + Brittney 4EVA." We’ll go with the first example, since we found the second one carved into the side of a maple tree and we’re not actually sure if it’s public domain.
If you want to multiply a + b and c + d, the FOIL method tells you how to do exactly that. The acronym—see, we weren't just yelling at you in all caps—stands for First, Outside, Inside, Last. It means that you should multiply the first two terms together (a × c = ac), then add that to the product of the two outer terms (a × d = ad), then add the product of the innermost terms (b × c = bc), and finally add the product of the last two (b × d = bd). Here’s your result:
ac + ad + bc + bd
This may not look too helpful right now, but this thing will be a life-saver once you’ve got a problem with a few numbers to plug in.
Okay, that’s a wrap on FOIL for now. A Reynolds Wrap.