Help Algebra
Help algebra.com: Rectangular Coordinates
The parts of the coordinate plane are described and plotting ordered pairs is demonstrated with several examples. The four quadrants of the coordinate plane are also defined.
Tech Target
Whatis.com: Cartesian Coordinates
This site from Whatis.com provides a great definition of cartesian coordinates. The definition is medium-sized in length and has links to additional information as well.
Paul Dawkins
Paul's Online Notes: Algebra: Graphing
Detailed math tutorial features notes and examples that take a look at the Cartesian (or Rectangular) coordinate system. Provides definitions of ordered pairs, coordinates, quadrants, and x and y-intercepts.
CK-12 Foundation
Ck 12: Polar Form of a Complex Number
[Free Registration/Login may be required to access all resource tools.] Here you will learn how to convert complex numbers from rectangular form to polar form. You will also explore the graphs of complex numbers on a polar graph.