EngageNY
Tangent Segments
What's so special about tangents? Learners first explore how if a circle is tangent to both rays of an angle, then its center is on the angle bisector. They then complete a set of exercises designed to explore further properties and...
Curated OER
Building Big and Strong
Middle and high schoolers explore the concepts of architectural rigidity. They analyze a variety of polygons, and explain why some shapes add more strength to structures than others. The PBS video, "Building Big," is utilized in this plan.
Curated OER
Why Doesn't SSA Work?
Students investigate the relationship between angles and their sides. In this geometry activity, students prove why SSA does not work as a true angle side relationship theorem.
Curated OER
Polygons All Around Us!
High schoolers explore the concept of polygon properties. For this polygon properties lesson, students draw polygons with different numbers of sides such as pentagons, octagons, hexagons, etc. High schoolers identify different geometric...
Curated OER
Tangram Perimeters
Students work together to make figures out of tangram squares. In groups, they calculate the measurements they need and apply the Pythagorean Theorem. They complete a worksheet solving equations using the theorem and review their answers.
Sophia Learning
Sophia: Using Corresponding Parts of Congruent Triangles
This lesson will demonstrate the use of CPCTC in triangle congruency proofs.
Khan Academy
Khan Academy: Proofs With Transformations
Explore different ways of proving some theorems about lines and angles. Some transformations are used.
Jim Loy
Jim Loy's Mathematics Page: Congruence of Triangles
Find explanations of the ways to prove triangles are congruent. There is a link for Congruence Of Triangles, Part II to find the proofs of some ways to prove congruence of triangles from other postulates (i.e. Assume SAS prove ASA).
Illustrative Mathematics
Illustrative Mathematics: g.co Reflections and Isosceles Triangles
This task has learners link their intuitive notions of symmetries of a triangle with statements proving that said triangle is unmoved by applying certain rigid transformations. The mechanism through which students do this is via...
Oswego City School District
Regents Exam Prep Center: Theorems and Postulates for Geometry
Here is a partial list of theorems, postulates, and properties.
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: Cpctc
[Free Registration/Login Required] This flipchart looks into the concept of CPCTC with triangles, using proofs. This flipchart has interactive parts, video, and voting.