Texas A&M University
Wtamu Virtual Math Lab: College Algebra: Circles
Use this tutorial to learn about the standard-form equation for a circle. Several step-by-step solutions and examples help you understand the part of the circle and how they relate to the equation.
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.