Illustrative Mathematics
Illustrative Mathematics: G Co, G Srt Seven Circles I
In this task, seven pennies are placed in a circle so that they are all touching one in the center and their neighbors. The question is whether this will work with other equally-sized circles. Aligns with G-SRT.C and G-CO.C.10.
Illustrative Mathematics
Illustrative Mathematics: G Co Classifying Triangles
The goal of this task is to help students synthesize their knowledge of triangles where only two of the vertices have been given. They will need to know that a triangle inscribed in a circle, with a diameter of the circle as one side, is...
Illustrative Mathematics
Illustrative Mathematics: G Co Midpoints of Triangle Sides
The goal of this task is to use similarity transformations to relate two triangles. The triangles are obtained by taking midpoints of two sides of a given triangle. Aligns with HSG-CO.C.10.
Illustrative Mathematics
Illustrative Mathematics: G Srt Finding the Area of an Equilateral Triangle
This task examines how to calculate the area of an equilateral triangle two ways: using triangle congruence and using trigonometric ratios. Aligns with G-CO.C.10 and G-SRT.C.
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...
CK-12 Foundation
Ck 12: Geometry: Pythagorean Theorem and Pythagorean Triples
[Free Registration/Login may be required to access all resource tools.] Apply the Pythagorean Theorem and its converse. Includes videos, exercises, links to interactive activities, etc.
Math Planet
Math Planet: Geometry: Proofs Using Algebra
Examples and a video lesson help to explain proofs and logic. [1:57]
Math Planet
Math Planet: Geometry: Conjecture
Conjecture is explained through examples and a video lesson. [0:41]
CK-12 Foundation
Ck 12: Geometry: Triangle Relationships Study Guide
[Free Registration/Login may be required to access all resource tools.] This study guide reviews terminology for triangles, triangle properties, different types of triangles, and interior and exterior angle theorems.
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: Pythagorean Theorem Study Guide
[Free Registration/Login may be required to access all resource tools.] This study guide is an overview of the Pythagorean theorem and its converse, Pythagorean triples, and proving the distance formula.
CK-12 Foundation
Ck 12: Geometry: Proportionality Relationships Study Guide
[Free Registration/Login may be required to access all resource tools.] This study guide looks at proportionality theorems for triangles and parallel lines intersected by transversals.
CK-12 Foundation
Ck 12: Geometry: Two Column Proofs Intermediate
[Free Registration/Login may be required to access all resource tools.] This concept teaches students how to write two-column proofs, and provides proofs for the Right Angle Theorem, Same Angle Supplements Theorem, and Vertical Angles...
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.
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: Triangle Inequalities
Explains the basic concept of triangle inequalities with step-by-step instructions and methods for solving specific problems on your own relating to this topic.
Geometry Help
Geometry Help: Isosceles Triangles
Explains the basic concept of isosceles triangles with step-by-step instructions and methods for solving specific problems on your own relating to this topic.
Geometry Help
Geometry Help: Congruent Triangles
Explains the basic concept of congruent triangles with step-by-step instructions and methods for solving specific problems on your own relating to this topic.
Khan Academy
Khan Academy: Proofs With Transformations
Explore different ways of proving some theorems about lines and angles. Some transformations are used.
Math Open Reference
Math Open Reference: Congruent Triangles
A complete reference guide to congruent triangles. It provides definitions, examples, and an interactive activity that enhances further explanation. Includes links to related topics.
CK-12 Foundation
Ck 12: Interactive Geometry: 4.6 Applications of Triangle Theorems
Explore applications of triangle theorems.