Cuemath
Cuemath: Euclidean Geometry
Explore the world of Euclidean geometry by understanding euclidean and non-euclidean geometry, the postulates and axioms, and how to apply them while solving problems. Check-out the solved examples for better understanding and try your...
University of St. Andrews (UK)
University of St. Andrews: Non Euclidean Geometry
The University of St. Andrews in Scotland provides an excellent site explaining Non-Euclidean geometry.
Mathigon
Mathigon: Geometry: Euclidean Geometry: Definitions
This lesson focuses on Euclidean Geometry terminology; such as line, point, line segment, congruence, circle, radius, ray, and more. It defines each term and provides an example of each.
Mathigon
Mathigon: Euclidean Geometry: Origami and Paper Folding
This lesson focuses on a different way to construct geometric figures without tools, Origami. The goal is to make objects out of one or more sheets of paper, without any additional tools like glue or scissors. You can create incredibly...
Wolfram Research
Wolfram Math World: Geometry
This MathWorld tutorial provides detailed overviews of the concepts and theorems associated with geometry. Most of the Math World sites are extensive and some require higher math knowledge to understand, links to terms and topics are...
Mathigon
Mathigon: Euclidean Geometry: Euclid's Axioms
This lesson focuses on Euclid's Axioms, simple, intuitive statements, that everyone agrees are true. An axiom(or postulate) is a mathematical statement that is regarded as "self-evident" and accepted without proof. A key part of...
Mathigon
Mathigon: Euclidean Geometry: Geometric Construction
This lesson focuses on the history of geometric construction beginning with Euclid's Axioms to the simple tools such as the straight edge and the compass.
Mathigon
Mathigon: Euclidean Geometry: Introduction
Mathematicians in ancient Greece were amazed by mathematical patterns, and wanted to explore and explain them. They began to study mathematics just "for fun" without a specific application in mind. One of these mathematicians, Thales of...
Oswego City School District
Regents Exam Prep Center: Lines and Planes
Use these resources in preparing instruction on undefined terms (points, lines, and planes), theorems relating lines and planes, and Euclidean and non-Euclidean geometry. You'll find three lessons on the aforementioned subject areas, an...
Wikimedia
Wikipedia: Hyperbolic Geometry
This encyclopedia entry from Wikipedia offers a discussion on hyperbolic geometry. The site explains how the hyperbolic geometry plane is represented in two dimensions and how lines in the plane must be drawn. Other types of models for...
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Hyperbolic Geometry
Dr. Math, responds to a question fro a nineth grade stduent who wants to understand hyperbolic geometry. The Dr. uses descriptive analogies in attempts to unravel why triangles in hyperbolic geometry have less than 180 degrees in them.
Wolfram Research
Wolfram Mathworld: Elliptic Geometry
MathWorld offers a brief definition of elliptic geometry and including a brief discussion of its relationship to Euclidean geometry, with links to other related definitions.
Cut the Knot
Cut the Knot!: Interactive Mathematics: Geometry Articles, Theorems, Problems
Contains over five hundred Geometry articles, problems, puzzles, and games. Some sites relating to circles are provided within this list.
University of California
University of California: Geometry in Action
This page collects various areas in which ideas from discrete and computational geometry (meaning mainly low-dimensional Euclidean geometry) meet some real-world applications.
Wikimedia
Wikipedia: Spherical Geometry
Wikipedia, a publicly-maintained encyclopedia, provides an explanation of spherical geometry along with a listing of its most important uses.
Boston University
Fractal Geometry of the Mandelbrot Set Ii
This web site addresses counting and adding in fractal operations, as well as the role of the Fibonacci sequence in fractal geometry.
Wolfram Research
Wolfram Math World: Euclid: The Elements
The classic treatise in geometry written by Euclid is presented in English. It is the textbook used for more than 1,000 years in western Europe.
Oswego City School District
Regents Exam Prep Center: Indirect Euclidean Proofs
This Oswego City School District Regents Exam Prep site shows you how to proof something by showing that it is false. This look at indirect proofs includes a practice and a teacher resource page, which features a warm-up activity.
Oswego City School District
Regents Exam Prep Center: Writing a Proof: Direct Euclidean Proofs
This site is a look into the world of geometric proofs. You'll learn what a proof is and about the different types of proofs. Try the practice page to check your understanding. Teachers can check out the teacher resources for lesson and...
Wolfram Research
Wolfram Math World: Spherical Geometry
Site provides a brief explanation of the discipline of Spherical Geometry along with many links to spherical geometry topics.
University of Illinois
University of Illinois Urbana Champaign: Torus Math: Spherical Geometry Demo
A java applet on this site illustrates the principles or spherical geometry.
Oswego City School District
Regents Exam Prep Center: Theorems and Postulates for Geometry
Here is a partial list of theorems, postulates, and properties.
Wolfram Research
Wolfram Math World: Hyperbolic Geometry
Hyperbolic Geometry is discussed here with specifics on the lines in this geometry. The equations of the lines are represented as well as a desription of the lines. The site has links to other non-Euclidean Geometries.
Math Words
Math words.com: Elliptic Geometry
The basic definition for what elliptic geometry is is found here.