CK-12 Foundation
Ck 12: 1.5 From Quadratics to Complex Numbers
This section introduces imaginary and complex numbers in the context of solutions to quadratic equations that don't have real-number solutions.
Math Is Fun
Math Is Fun: The Evolution of Numbers
Discusses what numbers are and how our understanding of them has evolved over thousands of years, from simple counting to negative numbers and irrational numbers, for example. Includes a set of practice questions where students identify...
CK-12 Foundation
Ck 12: Algebra Ii: 1.6 the Complex Plane
This section includes operations with imaginary and complex numbers and plotting numbers on the complex plane.
Cut the Knot
Cut the Knot!: What Is a Number?
Casual and clear but definitely upper-level discussion of rational, real, imaginary, and several other types of numbers. Links to related sites.
New York Times
New York Times: Steven Strogatz on the Elements of Math Series the New York Times
[Free Registration/Login Required] On this site, Cornell University mathematics professor, Steven Strogatz, shares his 15-part series of columns on the elements of math. He investigates topics ranging from negative numbers to subtraction...