Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Co Why Does Sas Work?

For Teachers 9th - 10th Standards
In this task, students must explain the given reasoning for why triangle ABC is congruent to triangle DEF using the language of reflections. Aligns with G-CO.B.8.
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Co Why Does Sss Work?

For Teachers 9th - 10th Standards
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....
Article
Mocomi & Anibrain Digital Technologies

Mocomi: Types of Triangles

For Students 2nd - 8th Standards
Explore the different types of triangles and other properties.
Unit Plan
Sophia Learning

Sophia: Equilateral Triangle Interior Angles Practice Problems: Lesson 5

For Students 9th - 10th
This lesson will provide practice problems that involve solving for unknown angle and side measures of equilateral triangles. It is 5 of 5 in the series titled "Equilateral Triangle Interior Angles Practice Problems."
Handout
Math Open Reference

Math Open Reference: Equilateral Triangle

For Students 9th - 10th Standards
Learn about equilateral triangles with this helpful reference tool. Provides a detailed definition, examples, and an interactive activity that enhances further explanation. Includes links to related topics.
Whiteboard
ClassFlow

Class Flow: Congruence in Triangles

For Teachers 9th - 10th Standards
[Free Registration/Login Required] This lesson helps teach congrence in triangles. Includes practice with postulates, theorems, and logical reasoning.
Handout
Sonoma State University

Sonoma State University: Parallel Lines and Similar and Congruent Triangles

For Students 9th - 10th Standards
This site defines parallel lines, parallel lines cut by a transverse, and congruent triangles. It also contains links for related terms.
Unit Plan
University of Saskatchewan (Canada)

University of Saskatchewan: Triangles

For Students 9th - 10th
This site from the University of Saskatchewan provides an explanation of similar triangles, the Pythagorean theorem, and the distance between arbitrary points in a plane. Example problems for each of these concepts are provided.
Whiteboard
ClassFlow

Class Flow: Congruent Triangles, Bi Conditional Statements

For Teachers 9th - 10th Standards
[Free Registration/Login Required] This flipchart contains an introduction to congruent triangles. It also introduces logic (p->q) including bi-conditional statements. A challenge is presented to students.
Whiteboard
ClassFlow

Class Flow: Congruency

For Teachers 9th - 10th Standards
[Free Registration/Login Required] Here are many variations of congruent triangles displayed for students to test their knowledge.
Interactive
Mangahigh

Mangahigh: Shape: Congruent Triangles

For Students 9th - 10th Standards
Explain how two triangles are congruent.
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: 8.g Congruent Triangles

For Teachers 8th Standards
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.
Activity
Analyze Math

Analyze Math: Congruent Triangle Problems

For Students 9th - 10th Standards
The geometry tutorial investigates congruent triangles. The activity has several examples with detailed solutions.
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: g.co Reflections and Isosceles Triangles

For Teachers 9th - 10th Standards
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...
Activity
Free Math Help

Free Math Help: Congruent Triangles

For Students 9th - 10th Standards
Students learn about congruent triangles. The tutorial consists of definitions and sample exercises with solutions.
PPT
Sophia Learning

Sophia: Cpctc: Lesson 2

For Students 9th - 10th
This lesson will demonstrate the use of CPCTC in triangle congruencey proofs. It is 2 of 4 in the series titled "CPCTC."
Handout
Sonoma State University

Sonoma State University: Parallel Lines and Similar and Congruent Triangles

For Students 9th - 10th Standards
This site defines eleven theorems relating to parallel lines and similar and congruent triangles. Links to the theorems and relevant term descriptions are provided.
Handout
Homeschool Math

Homeschool Math: Area of Right Triangles

For Students 6th - 8th
This lesson presents the idea that the area of any right triangle is exactly half of a certain rectangle, and contains varied exercises for students.
Study Guide
SEDL

The Timss Mathematics Segment: Geometry

For Students 4th - 8th Standards
This site explores the area of congruent triangles and how it is a difficult area to understand.
Activity
Texas Instruments

Texas Instruments: Math Today Ballooning Inside the Box

For Teachers 9th - 10th Standards
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...
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Srt Extensions, Bisections, Dissections in Rectangle

For Teachers 9th - 10th Standards
For this task, learners must draw a diagram from a verbal description and use their understanding of similar triangles to find the area of a quadrilateral. Aligns with G-SRT.B.5.
Handout
Science Struck

Science Struck: Similarity Statement in Geometry With Examples

For Students 9th - 10th Standards
Models how to write a similarity statement about different types of triangles and quadrilaterals.
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Gpe, G Srt Slope Criterion for Perpendicular Lines

For Teachers 9th - 10th Standards
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.
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Srt Tangent Line to Two Circles

For Teachers 9th - 10th Standards
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.

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