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.
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: Corner Circle
This is a "three star" geometry problem where prior knowledge of circles and triangles is recommended to solve this circle in the corner problem.
Maths Challenge
Maths challenge.net: Shaded Cross
Find the area of this tilted cross with your geometry skills.
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.
Other
Georgia Tech: The Four Color Theorem
An explanation and proof of the Four Color Map Theorem. Includes illustrative images and a plethora of information.
Alabama Learning Exchange
Alex: The Pythagorean Theorem in the Real World
The introduction of this lesson has students verifying the famous Pythagorean Theorem with a hands-on proof. Students will then apply the Theorem in one of two ways: by solving for the side lengths of a right triangle and by determining...
Other
Mathematical the Four Color Theorem and Computer Proof
This site describes the role of computer involvement in the four color map theorem.
ClassFlow
Class Flow: Circles Geometry
[Free Registration/Login Required] Students identify segments and lines related to circles and the properties of a tangent to a circle.
CK-12 Foundation
Ck 12: Geometry: Quadrilaterals That Are Parallelograms
[Free Registration/Login may be required to access all resource tools.] Prove a quadrilateral is a parallelogram.
Cuemath
Cuemath: Angle Bisector Theorem
This short lesson focuses more on the angle bisector theorem. Learn about the angle bisector theorem proof, triangle angle bisector theorem, how to construct angle bisector, and other interesting properties and facts around angle bisectors.
Cuemath
Cuemath: Midsegment of a Triangle
This mini-lesson explores the world of the midsegment of a triangle by finding the answers to questions like what is midsegment of a triangle, triangle midsegment theorem, and proof with the help of interactive questions.
Cuemath
Cuemath: Triangle Inequality Theorem
This lesson explores triangle inequality theorem, triangle inequality theorem-proof, and triangle inequality theorem problems. Try the hands-on triangle inequality theorem calculator and interactive problems to have a better...
Maths Challenge
Maths challenge.net: Cables
This is a proof problem, considered a "three star" geometry problem requiring knowledge of proofs and properties of circles to solve this problem with cables in duct problem.
Maths Challenge
Maths challenge.net: Radical Axis
This is a "three star" geometry problem requiring knowledge of proofs and properties of circles. Students will use the given definition of radical axis and prior knowledges to prove a way to find a radical axis.
Cut the Knot
Cut the Knot!: The Law of Cosines (Cosine Rule)
This site from Cut The Knot provides an overview of the law of cosines, complete with an explanation of the law and a proof of the law.
Sophia Learning
Sophia: Cpctc: Lesson 2
This lesson will demonstrate the use of CPCTC in triangle congruencey proofs. It is 2 of 4 in the series titled "CPCTC."
ClassFlow
Class Flow: Collinearity, Betweenness, and Assumptions
[Free Registration/Login Required] This flipchart is aligned with the book Geometry for the Enjoyment and Challenge. This lesson is collinearity, betweenness, and assumptions to help in the development of the study of proofs.
Oswego City School District
Regents Exam Prep Center: Triangle Inequality Theorems
This tutorial discusses triangle inequality and provides practice problems for students to try out their skills. The teacher resource page contains a lesson plan for a yummy activity involving licorice.
Cuemath
Cuemath: 30 60 90 Triangle
In this lesson, learn all about the 30-60-90 triangle. Learn about its sides, its area, and the rules that apply to these triangles. Includes simulations and practice questions.
Cuemath
Cuemath: Hypotenuse Leg Theorem
Explore the world of the hypotenuse leg theorem in this mini-lesson. Provides a definition, examples, and practice questions with answers that help with understanding their properties.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Proof the Inscribed Angle Theorem
Dr. Math gives a student a hint on how to prove that an inscribed angle is equal to 1/2 the central angle. You should know what the central angle and inscribed angle are to utilize this site.
Dartmouth College
Dartmouth College: The Different Styles of Euclid and Copernicus
A history of the differences between Euclid's and Copernicus's methods of proving geometric ideas.
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