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.
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.
Khan Academy
Khan Academy: Line and Angle Proofs
Explore different ways of proving some theorems about lines and angles. Some transformations are used. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video, or receive hints.
Illustrative Mathematics
Illustrative Mathematics: G C, G Co Tangent Lines and the Radius of a Circle
In this task, students are shown a circle with center O and point P on the circle. L is a line that is a tangent to the circle at P. They must show that line OP is perpendicular to line L. Aligns with G-C.A.2, G-CO.A, and G-CO.C.9.
Illustrative Mathematics
Illustrative Mathematics: G Co Points Equidistant From Two Points in the Plane
In this task, students are shown a line segment that is bisected at a right angle by a second line. They are asked to prove statements about this geometric construction. Includes a GeoGebra worksheet that can be used by the instructor to...
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]
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...
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: Intersecting Lines and Angles
Explains the basic concept of intersecting lines and angles with step-by-step instructions and methods for solving specific problems on your own relating to this topic.
Geometry Help
Geometry Help: What Are Parallel Lines in Geometry?
Explains the basic concept of parallel lines in Geometry 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 Angles
Learn about congruent angles with this handy reference guide. Provides a detailed definition, examples, and an interactive activity that enhances further explanation. Includes links to related topics.
CK-12 Foundation
Ck 12: Interactive Geometry: 4.3 Applications of Line and Angle Theorems
Learn the four categories of theorems that have to do with lines and angles.
CK-12 Foundation
Ck 12: Interactive Geometry: 4.4 Theorems About Triangles
Discover some theorems about triangles.
CK-12 Foundation
Ck 12: Interactive Geometry: 4.1 Theorems and Proofs
Understand theorems and proofs as they relate to geometry.