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Complex Numbers Primer

Before I get started on this let me first make it clear that this document is not intended to teach you everything there is to know about complex numbers. That is a subject that can (and does) take a whole course to cover. The purpose of this document is to give you a brief overview of complex numbers, notation associated with complex numbers, and some of the basic operations involving complex numbers.

This document has been written with the assumption that you’ve seen complex numbers at some point in the past, know (or at least knew at some point in time) that complex numbers can be solutions to quadratic equations, know (or recall) \(i=\sqrt{-1}\), and that you’ve seen how to do basic arithmetic with complex numbers. If you don’t remember how to do arithmetic I will show an example or two to remind you how to do arithmetic, but I’m going to assume that you don’t need more than that as a reminder.

For most students the assumptions I’ve made above about their exposure to complex numbers is the extent of their exposure. Problems tend to arise however because most instructors seem to assume that either students will see beyond this exposure in some later class or have already seen beyond this in some earlier class. Students are then suddenly expected to know more than basic arithmetic of complex numbers but often haven’t actually seen it anywhere and have to quickly pick it up on their own in order to survive in the class.

That is the purpose of this document. We will go beyond the basics that most students have seen at some point and show you some of the notation and operations involving complex numbers that many students don’t ever see once they learn how to deal with complex numbers as solutions to quadratic equations. We’ll also be seeing a slightly different way of looking at some of the basics that you probably didn’t see when you were first introduced to complex numbers and proving some of the basic facts.

The first section is a more mathematical definition of complex numbers and is not really required for understanding the remainder of the document. It is presented solely for those who might be interested.

The second section (arithmetic) is assumed to be mostly a review for those reading this document and can be read if you need a quick refresher on how to do basic arithmetic with complex numbers. Also included in this section is a more precise definition of subtraction and division than is normally given when a person is first introduced to complex numbers. Again, understanding these definitions is not required for the remainder of the document they are only presented so you can say you’ve seen it.

The remaining sections are the real point of this document and involve the topics that are typically not taught when students are first exposed to complex numbers.

So, with that out of the way, let’s get started…