Equation of a Circle
If a circle is centered at the origin, write an equation describing every point on the circle. Your equation should use the radius of the circle and the xcoordinate and ycoordinate of ANY point on the circle.

Related External Resources 
Examples of Equation of the Circle
These examples show how to find an equation and graph a circle based on different criteria.
School Bus Geometry
Determine the changes in the graph of a circle in this form of geometry.
Submit your idea for an investigation to InterMath.
