Education Development Center
Making Mathematics: Proof
This is a site which links to specific techniques of proving including conditional statements, proof by contradiction, mathematical induction, parity arguments, and the pigeonhole principle. The site contains a link to various example...
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: The Value of Two Column Proofs
This site explains why we prove things. The explanation gives real world scenarios and an everyday example of why we should learn how to prove things.
Varsity Tutors
Varsity Tutors: Hotmath: Practice Problems: Logic and Proof Exercises
Twenty-five problems cover the topic of logic and proof in different geometry settings. They are given with each step to the solution cleverly revealed one at a time. You can work each step of the problem then click the "View Solution"...
McGraw Hill
Glencoe Mathematics: Self Check Quiz on Reasoning & Proof
The online assessment demonstrates knowledge of concepts utilized in Geometry. The multiple choice questions test students on mathematical reasoning and proof.
Oswego City School District
Regents Exam Prep Center: Theorems and Postulates for Geometry
Here is a partial list of theorems, postulates, and properties.
Texas Education Agency
Texas Gateway: Connecting Postulates, Definitions, and Theorems
The student will distinguish the difference between undefined terms, definitions, postulates, conjectures, and theorems.
Mathigon
Mathigon: Axioms and Proof
Explore this course in logic, sets, and proof including topics of axioms, set theory, and proof by contradiction and induction.
Illustrative Mathematics
Illustrative Mathematics: G Co, G Srt Congruence of Parallelograms
In this task, a student has learned the SSS and SAS congruence tests for triangles and wonders if these tests might work for parallelograms. Aligns with G-CO.C.11 and G-SRT.B.5
Illustrative Mathematics
Illustrative Mathematics: G Co Midpoints of the Sides of a Paralellogram
Suppose that ABCD is a parallelogram and that M and N are the midpoints of lines AB and CD respectively. Students are asked to prove that MN=AD, and that the line MN is parallel to line AD. Aligns with G-CO.C.11.
Illustrative Mathematics
Illustrative Mathematics: G Co Parallelograms and Translations
In this task, students apply the definition of a parallelogram in the context of a geometric construction. Aligns with G-CO.C.11.
Illustrative Mathematics
Illustrative Mathematics: G Co Is This a Parallelogram?
In the pictured quadrilateral, opposite sides are congruent and students must explain whether this makes it a parallelogram. Aligns with G-CO.C.11.
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 Open Reference
Math Open Reference: Congruence
A complete reference guide to congruence including congruent triangles and polygons. It provides definitions, animation, and interactive activities that enhance further explanation.
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: Working With Logic
How to determine if a logical statement is true or false is explained through examples and a video lesson. [2:46]
Math Planet
Math Planet: Geometry: Conjecture
Conjecture is explained through examples and a video lesson. [0:41]
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.
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: 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...
CK-12 Foundation
Ck 12: Geometry: Parallelograms Study Guide
This study guide on parallelograms covers types of quadrilaterals, properties of parallelograms and theorems that describe them, how to identify parallelograms, and special types of parallelograms. It is available for download with free...
National Council of Teachers of Mathematics
Nctm: Illuminations: Proof Without Words: Pythagorean Theorem
This applet proves the Pythagorean Theorem "without words" using geometry.
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.
Khan Academy
Khan Academy: Proofs With Transformations
Explore different ways of proving some theorems about lines and angles. Some transformations are used.