After reviewing the process of solving quadratic and cubic equations, a definition of an imaginary number is given. Also included is a demonstration of simplifying powers of the imaginary number and writing complex numbers. Examples are...

This section introduces imaginary and complex numbers in the context of solutions to quadratic equations that don't have real-number solutions.

This site from a professor at Clark University teaches you about complex numbers.

Multiply complex numbers by single terms that are either real or imaginary. Students receive immediate feedback and have the opportunity to try questions repeatedly or receive hints.

Contains a lesson and practice exercises about complex numbers in a complex plane.

In this lesson, you will learn about complex numbers and imaginary numbers. Included are solved examples and interactive questions for review.

Casual and clear but definitely upper-level discussion of rational, real, imaginary, and several other types of numbers. Links to related sites.

This site from Friesian.com contains a detailed definition of imaginary numbers along with a few examples.

This site from the University of Toronto contains revelant information regarding imaginary number appliances to the real world.