Cool Math
Coolmath: Geometry & Trig Reference
Math formulas, definitions, properties, diagrams and examples from Geometry and Trigonometry.
Illustrative Mathematics
Illustrative Mathematics: G Gpe, G Co, G Srt Unit Squares and Triangles
In this task, students are shown three unit squares and two line segments connecting two pairs of vertices. They are asked to find the area of a triangle formed by intersecting lines. They can solve it using coordinate geometry or...
Illustrative Mathematics
Illustrative Mathematics: G Gpe a Midpoint Miracle
In this task, students are asked to draw a quadrilateral so that no two sides are congruent, no two angles are congruent, and no two sides are parallel. The task gives students the opportunity to prove that if we join the midpoints of a...
TED Talks
Ted: Ted Ed: How Many Ways Are There to Prove the Pythagorean Theorem?
Betty Fei details these three famous Pythagorean theorem proofs.
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...
Math Planet
Math Planet: Geometry: Proofs Using Algebra
Examples and a video lesson help to explain proofs and logic. [1:57]
CK-12 Foundation
Ck 12: Geometry: Indirect Proof in Algebra and Geometry
[Free Registration/Login may be required to access all resource tools.] This concept teaches students how to write an indirect proof and provides examples of indirect proofs in Algebra and Geometry.
CK-12 Foundation
Ck 12: Geometry: Indirect Proof in Algebra and Geometry
[Free Registration/Login may be required to access all resource tools.] Write algebraic and geometric indirect proofs.
Rice University
Rice University: Cynthia Lanius: History of Geometry
Different cultures' contributions to Geometry are discussed.
CK-12 Foundation
Ck 12: Geometry: Proofs Study Guide
[Free Registration/Login may be required to access all resource tools.] This study guide reviews proofs: algebraic proof, properties of congruence, and geometric proofs (two-column).
CK-12 Foundation
Ck 12: Geometry: Basics of Geometry Study Guide
This study guide on Geometry covers some key vocabulary, drawing and labeling diagrams, describing geometric figures, and basic postulates for points, lines, planes, and intersections. It is available for download with free registration.
Thinkport Education
Math by Design: Pythagorean Theorem [Pdf]
Use right angle concepts to solve problems amid geometric relationships.
National Council of Teachers of Mathematics
Nctm: Illuminations: Proof Without Words: Pythagorean Theorem
This applet proves the Pythagorean Theorem "without words" using geometry.
Shodor Education Foundation
Shodor Interactivate: Squaring the Triangle
Learn about how the Pythagorean Theorem works through investigating the standard geometric proof.
Math Open Reference
Math Open Reference: Introduction to Coordinate Geometry
A complete reference guide to coordinate geometry. It provides definitions and examples that enhance further explanation. Includes links to related topics.
Geometry Help
Geometry Help: Hinge Theorem
Provides a detailed definition of the Hinge Theorem with step-by-step instructions and methods for solving problems on your own.
Geometry Help
Geometry Help: Inscribed Shapes
Explains the basic concept of inscribed shapes with step-by-step instructions and methods for solving specific problems on your own relating to this topic.
Geometry Help
Geometry Help: Circles
Explains the basic concept of circles with step-by-step instructions and methods for solving specific problems on your own relating to this topic.
National Council of Teachers of Mathematics
Nctm: Illuminations: A Geometric Investigation of (A + B)2
This interactive demonstrates why (a + b)2 = a2 +2ab + b2.
Khan Academy
Khan Academy: Proofs With Transformations
Explore different ways of proving some theorems about lines and angles. Some transformations are used.
Cuemath
Cuemath: Midpoint Theorem
A comprehensive guide for learning all about plane shapes with definitions and solved examples.
CK-12 Foundation
Ck 12: Interactive Geometry: 11.1 Descriptions of Events
In a coordinate proof, geometric statements using algebra and the coordinate plane.
CK-12 Foundation
Ck 12: Interactive Geometry: 10.3 Equations of Parabolas
Learn about equations of parabolas.
CK-12 Foundation
Ck 12: Interactive Geometry: 10.2 Equations of Circles
Derive the equation of a circle with the help of the Pythagorean Theorem.