University of Cambridge
University of Cambridge: Nrich: Seven Sticks
On this one page website sharpen your logic, triangle properties, and pattern recognition skills while working on this challenge. The solution is available to double check your solution.
Illustrative Mathematics
Illustrative Mathematics: 8.g Congruent Triangles
In this task, 8th graders investigate congruence and transformations of two triangles on a coordinate grid. Includes a GeoGebra worksheet that the teacher can use for demonstration purposes. Aligns with 8.G.A.2.
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...
Curated OER
Nova Scotia Dept. Of Education: Mathematics 8: Geometry Diagrams
A collection of diagrams that complement Mathematics 8, a Grade 8 Math text, have been posted here. The diagrams were created using The Geometer's Sketchpad,
Illustrative Mathematics
Illustrative Mathematics: G Srt, G Mg How Far Is the Horizon?
Some friends are at the beach looking out onto the ocean on a clear day and they wonder how far away the horizon is. A second problem asks how far the horizon would be from the top of a mountain. Students must also answer a question...
Free Math Help
Free Math Help: Congruent Triangles
Students learn about congruent triangles. The tutorial consists of definitions and sample exercises with solutions.
Alabama Learning Exchange
Alex: "Tan"
The Chinese character mark formerly known as "Tan" is the first of two lessons to introduce first grade students to geometry using tangrams. This lesson incorporates history, math, and language arts. In this lesson students will be able...
Illustrative Mathematics
Illustrative Mathematics: G Co Why Does Asa Work?
In triangles ABC and ABD, we are given that angle BAC is congruent to angle BAD and angle ABC is congruent to angle ABD. Show that the reflection of the plane about line AB maps triangle ABD to triangle ABC. Aligns with G-CO.B.8.
SEDL
The Timss Mathematics Segment: Geometry
This site explores the area of congruent triangles and how it is a difficult area to understand.
Illustrative Mathematics
Illustrative Mathematics: 8.g, G Gpe, G Srt, G Co Is This a Rectangle?
For this task, students are given four sets of coordinate pairs and are asked to determine if they represent a rectangle. Aligns with 8.G.A, 8.G.B, G-CO.B, G-GPE.B, and G-SRT.B.5.
Illustrative Mathematics
Illustrative Mathematics: G Co Why Does Sss Work?
In this task, students must show that two triangles are congruent given a set of steps which produce a rigid transformation of the plane. Includes an experimental GeoGebra worksheet that instructors can use to demonstrate the task....
Oswego City School District
Regents Exam Prep Center: Theorems and Postulates for Geometry
Here is a partial list of theorems, postulates, and properties.
Texas Instruments
Texas Instruments: Math Today Ballooning Inside the Box
In this activity Using the USATODAY infograph, "Ballooning inside the box", students will explore geometric relationships using similar triangles. Identifying triangles with two pairs of congruent angles to explore similarity properties...
Oswego City School District
Regents Exam Prep Center: Working With Sets and Venn Diagrams
A collection of activities that help students understand number relationships by using Venn diagrams to solve math problems. Practice problem solving skills in the interactive practice. Then, follow up with a classroom activity using the...
Illustrative Mathematics
Illustrative Mathematics: G Gpe, G Srt Slope Criterion for Perpendicular Lines
The goal of this task is to use similar triangles to establish the slope criterion for perpendicular lines. Aligns with HSG-GPE.B.5 and HSG-SRT.B.5.
Illustrative Mathematics
Illustrative Mathematics: G Srt Tangent Line to Two Circles
The purpose of this task is to use similar triangles and setting up a proportion in order to calculate a side length. Aligns with G-SRT.B.5.
National Council of Teachers of Mathematics
The Math Forum: Line Symmetry
This site from The Math Forum is a great site if you are looking for activities to engage your students in learning about line symmetry. Peruse this collection of activities for one or two or four that would be right for your students....
Illustrative Mathematics
Illustrative Mathematics: G Srt Folding a Square Into Thirds
The goal of this task is to apply knowledge about similar triangles in order to understand an origami construction: trisection of the side of a square. Aligns with G-SRT.B.5.
Alabama Learning Exchange
Alex: Tan Ii
The Chinese character mark for Tan II (pronounced she-tow-bah) is the second of two lessons to introduce first grade students to geometry using tangrams. This lesson incorporates history, math, and language arts. In this lesson students...
Illustrative Mathematics
Illustrative Mathematics: G Srt Bank Shot
This task asks students to use similarity to solve a pool table problem. Students must use the fact from physics that when an object bounces off of a wall, the angle of incidence equals the angle of reflection. Aligns with G-SRT.B.5.
CK-12 Foundation
Ck 12: Geometry: Third Angle Theorem Grades 8 10
[Free Registration/Login may be required to access all resource tools.] Apply the Third Angle Theorem.
CK-12 Foundation
Ck 12: Geometry: Perimeter and Area Study Guide
[Free Registration/Login may be required to access all resource tools.] This study guide looks at the definitions and units for perimeter, area, and circumference, and at the perimeter and area of different shapes, including regular...
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."
Sophia Learning
Sophia: Corresponding Parts: Lesson 5
This lesson will define the phrase corresponding parts (e.g. angles, sides, etc.). It is 5 of 5 in the series titled "Corresponding Parts."