Wolfram Research
Wolfram Math World: Circles
This site provides definitions for a wide range of topics dealing with circles.
Maths Challenge
Maths challenge.net: Cables
This is a proof problem, considered a "three star" geometry problem requiring knowledge of proofs and properties of circles to solve this problem with cables in duct problem.
Maths Challenge
Maths challenge.net: Radical Axis
This is a "three star" geometry problem requiring knowledge of proofs and properties of circles. Students will use the given definition of radical axis and prior knowledges to prove a way to find a radical axis.
Sophia Learning
Sophia: Types of Proofs: Lesson 3
This lesson will introduce flow chart proofs, paragraph proofs, and two-column proofs, and explain the similarity and differences between the different types of proofs. It is 3 of 5 in the series titled "Types of Proofs."
ClassFlow
Class Flow: Congruency
[Free Registration/Login Required] Here are many variations of congruent triangles displayed for students to test their knowledge.
Math Is Fun
Math Is Fun: Congruent
The resource investigates congruent shapes. Examples and definitions are included.
Math Is Fun
Math Is Fun: Circle
Students learn about the terminology and formulas associated with circles. The learning resource consists of diagrams and examples.
Shmoop University
Shmoop: Basic Geometry: Circles
The geometry resource explores the different parts of a circle. Definitions and examples are included.
Math Is Fun
Math Is Fun: Congruent Angles
Students learn about congruent angles. A definition, example, and tips are included.
University of British Columbia
University of British Columbia: Proof of the Pythagorean Theorem
A geometric model that proves the Pythagorean Theorem in a step-by-step diagram that students can advance at their own pace. Requires Java.
Wolfram Research
Wolfram Math World: Postulate
This MathWorld site defines postulates, and explains how and where they are used in mathematics. The site has numerous links to related terms.
Cut the Knot
Cut the Knot!: Proofs in Mathematics
This site provides an explanation of mathematical proofs. It also has links to different types of proofs.
Math Open Reference
Math Open Reference: Circumcircle
A handy reference guide to circumcircles. It provides definitions and examples that enhance further explanation. Includes links to related topics.
Michigan State University
Michigan State University: Biometrics: Hand Geometry
Students use hand geometry to prove their own identification.
National Council of Teachers of Mathematics
The Math Forum: Mathematics Teacher Bibliography: Circles
A bibliography of articles relating to circles published in the Mathematics Teacher is listed.
Oswego City School District
Regents Exam Prep Center: Formulas for Angles in Circles
Formulas and illustrations show the different kinds of angles created by intersecting tangents, secants, radii, and in combination.