Wolfram Research
Wolfram Math World: Central Angle
This page provides a brief definition of a central angle which is illustrated with a drawing. This site also contains related links.
CK-12 Foundation
Ck 12: Geometry: Properties of a Circle Study Guide
[Free Registration/Login may be required to access all resource tools.] This study guide reviews the terminology for circles (tangent, arcs, central angles) and the equation for a circle.