Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: 8.g Cutting a Rectangle Into Two Congruent Triangles

For Teachers 8th Standards
This task shows the congruence of two triangles formed by cutting a rectangle in half along the diagonal. Students are asked to investigate elements of congruence and transformations among the shapes. Aligns with 8.G.A.2.
Handout
Math Open Reference

Math Open Reference: Congruent Triangles

For Students 9th - 10th Standards
A complete reference guide to congruent triangles. It provides definitions, examples, and an interactive activity that enhances further explanation. Includes links to related topics.
Interactive
Math Open Reference

Math Open Reference: Congruence

For Students 9th - 10th Standards
A complete reference guide to congruence including congruent triangles and polygons. It provides definitions, animation, and interactive activities that enhance further explanation.
Activity
Varsity Tutors

Varsity Tutors: Hotmath: Practice Problems: Congruent Triangles and Triangle Relationships

For Students 9th - 10th Standards
Twenty-four problems cover the topics of congruent triangles and triangle relationships in various settings. They are given with each step to the solution cleverly revealed one at a time. You can work each step of the problem then click...
Activity
Texas Instruments

Texas Instruments: Congruent Triangles

For Teachers 9th - 10th Standards
This activity works with a PowerPoint presentation to have students answer questions as to what method a pair of triangles can be proven congruent: SSS, SAS, ASA, AAS, HL.
Unknown Type
Khan Academy

Khan Academy: Find Angles in Congruent Triangles

For Students 9th - 10th Standards
Given two triangles, determine whether they are congruent and use that to find missing angle measures.
Activity
Varsity Tutors

Varsity Tutors: Hotmath: Graphing Calculator: Congruent Triangles and Triangle Relationships

For Students 9th - 10th Standards
Practice using your graphing calculator for demonstrating congruent triangles. If you get stumped or if you would like to check your work, then select the View Solution button, which is located directly under each problem.
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Co, G Srt Congruence of Parallelograms

For Teachers 9th - 10th Standards
In this task, a student has learned the SSS and SAS congruence tests for triangles and wonders if these tests might work for parallelograms. Aligns with G-CO.C.11 and G-SRT.B.5
Activity
Texas Instruments

Texas Instruments: Isosceles Triangle

For Teachers 9th - 10th Standards
In this activity, students construct isosceles and equilateral triangles. They discover that if two sides of a triangle are congruent, then the angles opposite them are congruent. They understand that an equilateral triangle is also...
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Gpe, G Co, G Srt Unit Squares and Triangles

For Teachers 9th - 10th Standards
In this task, young scholars are shown three unit squares and two line segments connecting two pairs of vertices. They are asked to find the area of a triangle formed by intersecting lines. They can solve it using coordinate geometry or...
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Srt Joining Two Midpoints of Sides of a Triangle

For Teachers 9th - 10th Standards
In this task, students must prove that angles and triangles are congruent and that a parallel line passes through the midpoints of two sides of the larger triangle. Aligns with G-SRT.B.4.
Unit Plan
CK-12 Foundation

Ck 12: Congruence Statements

For Students 9th - 10th Standards
[Free Registration/Login Required] Students explore the concept of congruence statements by navigating through the interactive learning module and then answering questions that go along with the module. Students can also learn more about...
Activity
Beacon Learning Center

Beacon Learning Center: Congruent or Not?

For Students 3rd - 5th
Students explore congruent polygons in this interactive web lesson.
Interactive
Mangahigh

Mangahigh: Shape: Recognize Congruent Shapes

For Students 9th - 10th Standards
Determine whether shapes are congruent or similar.
Unit Plan
Math Open Reference

Math Open Reference: Triangles

For Students 9th - 10th Standards
A complete reference guide to types of triangles and triangle perimeter and area. It provides definitions and interactive animated activities that enhance further explanation.
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Gpe, G Srt Finding Triangle Coordinates

For Teachers 9th - 10th Standards
Given a picture of a triangle on a coordinate grid, students are asked to find the coordinates of points which divide line segments in a given ratio. Aligns with G-GPE.B.6 and G-SRT.B.5.
Handout
Math Open Reference

Math Open Reference: Similar Triangles

For Students 9th - 10th Standards
Learn about similar triangles with this helpful reference tool. Provides a detailed definition, examples, and an interactive activity that enhances further explanation. Includes links to related topics.
Website
National Council of Teachers of Mathematics

The Math Forum: Ask Dr. Math: Congruence and Triangles

For Students 9th - 10th Standards
This site gives a very thorough explanation of how to tell if two triangles are congruent. Dr. Math explains why SSS, SAS, ASA determine that two triangles are congruent. The Dr. gives a few exercises for the reader to try then gives the...
Handout
Jim Loy

Jim Loy's Mathematics Page: Congruence of Triangles

For Students 9th - 10th Standards
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).
eBook
Math Planet

Math Planet: Geometry: Congruent Triangles

For Students 9th - 10th Standards
Features a definition and a video lesson on congruent triangles with examples. [1:11]
eBook
CK-12 Foundation

Ck 12: Interactive Geometry: 6.3 Aa Triangle Similarity

For Students 9th - 10th Standards
If two triangles are similar, it means that all corresponding angle pairs are congruent and all corresponding sides are proportional. However, in order to be sure that two triangles are similar, you do not necessarily need to have...
eBook
CK-12 Foundation

Ck 12: Interactive Geometry: 6.5 Sss Triangle Similarity

For Students 9th - 10th Standards
Explore and understand two triangles that are similar.
eBook
CK-12 Foundation

Ck 12: Interactive Geometry: 6.4 Sas Triangle Similarity

For Students 9th - 10th Standards
Explore and understand triangle similarity.
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Co Why Does Asa Work?

For Teachers 9th - 10th Standards
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.

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