Maths Challenge
Maths challenge.net: Three Circles
This is a proof problem, considered a "three star" geometry problem requiring knowledge of proofs and properties of circles.
Maths Challenge
Maths challenge.net: Isosceles Trapezium
This is a "three star" geometry problem where prior knowledge of problem solving and thinking through proofs is recommended to solve this trapezoid inscribed in a semicircle problem.
Maths Challenge
Maths challenge.net: Right Angle Reasoning
A geometry problem for students to use their mathematical reasoning skills to explain a right triangle property.
Texas Education Agency
Texas Gateway: Using Logical Reasoning to Prove Conjectures About Quadrilaterals
Given conjectures about quadrilaterals, the student will use deductive reasoning and counter examples to prove or disprove the conjectures.
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...
Texas Education Agency
Texas Gateway: Constructing and Justifying Statements About Geometric Figures
Students will distinguish between undefined terms, definitions, postulates, conjectures, and theorems and investigate patterns to make conjectures about geometric relationships.
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...
OER Commons
Oer Commons: Mars: Proving the Pythagorean Theorem
This lesson is intended to help you assess how well learners are able to produce and evaluate geometrical proofs. PowerPoint slides are included with the lesson.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Building Two Column Proofs
Use this site to find details of how to construct a two column proof. Dr. Math responds to a question posed by a student and details the reasons for the order of steps and shows two different ways to do the same proof.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Order of a Proof
The site gives a diagram of steps to a proof. Dr. Math explains why the step order of a proof is important.
Science Education Resource Center at Carleton College
Serc: Pythagorean Theorem Investigations
In this activity, learners will gain an understanding of the Pythagorean theorem and will recognize the variety of ways in which theorems can be proved algebraically, geometrically and visually.
Maths Challenge
Maths challenge.net: Quadrilateral Parallelogram
A "three star geometry problem" requiring knowledge of how to complete geometric proofs and some prior math knowledge. This problem asks to prove that the mid points of any quadrilateral form a parallelogram.
Maths Challenge
Maths challenge.net: Unique Circle Equal Angles
A "three star geometry problem" - requiring the knowledge of biconditional statements and how to prove such problems.
Maths Challenge
Maths challenge.net: Odd Vertices
A "three star geometry problem" requiring knowledge of how to complete geometric proofs. The problem explains what the order of a vertex is and asks for the proof of a generalization.
Maths Challenge
Maths challenge.net: Coloured Strings
A "three star geometry problem" - requiring the knowledge of what a cuboid is and a some knowledge of how to do proofs.
Maths Challenge
Maths challenge.net: Parallelogram Property
A "three star geometry problem" requiring knowledge of how to complete geometric proofs properties of parallelogram.
Math Planet
Math Planet: Geometry: Converse of the Pythagorean Theorem and Special Triangles
The converse of the Pythagorean Theorem is examined through examples and a video lesson. [1:04]
Other
Math Court: A Game of Proving Things
This site contains a game to help students better learn how to write proofs. The game has several different levels. The game can be played online or cards and board may be printed and used in the classroom.
Math Planet
Math Planet: Geometry: If Then Statement
If-then statements are explained throught the use of examples and a video lesson. [1:16]
Mangahigh
Mangahigh: Shape: Proof of the Exterior Angle Theorem for a Triangle
Use your knowledge of exterior angles of a triangle to prove the theorem.
Mangahigh
Mangahigh: Shape: Inscribed and Central Angles in Circles
Use theorems to prove ideas of inscribed and central angles in circles.
Texas Education Agency
Texas Gateway: Using Logical Reasoning to Prove Statements Are True
Given statements about a geometric relationship, the student will distinguish between the undefined terms, definitions, postulates, conjectures, and theorems to prove the statements are true.
Other
Xah Lee: Some Theorems on Rotation and Translation
This site is for the purpose of using proofs for geometry. It helps by giving some useful theorems.
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.