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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...
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Lesson Plan
Illustrative Mathematics

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

For Teachers 9th - 10th Standards
In this task, students 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...
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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.
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Activity
Beacon Learning Center

Beacon Learning Center: Congruent or Not?

For Students 3rd - 5th
Students explore congruent polygons in this interactive web lesson.
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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, young scholars 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.
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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.
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PPT
Sophia Learning

Sophia: Triangle Congruence Theorem (Hl): Lesson 5

For Students 9th - 10th Standards
This lesson will present the Hypotenuse-Leg Triangle Congruence Theorem. It is 5 of 5 in the series titled "Triangle Congruence Theorem (HL)."
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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.
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Article
Mocomi & Anibrain Digital Technologies

Mocomi: Types of Triangles

For Students 2nd - 8th Standards
Explore the different types of triangles and other properties.
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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."
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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).
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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.
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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...
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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.
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eBook
CK-12 Foundation

Ck 12: Interactive Geometry: 6.4 Sas Triangle Similarity

For Students 9th - 10th Standards
Explore and understand triangle similarity.
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Unit Plan
Oswego City School District

Regents Exam Prep Center: Working With Sets and Venn Diagrams

For Students 2nd - 8th Standards
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...
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Activity
University of Cambridge

University of Cambridge: Nrich: Seven Sticks

For Students K - 1st Standards
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.
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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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Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Co Why Does Sas Work?

For Teachers 9th - 10th Standards
In this task, young scholars 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.
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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....
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Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Srt Finding the Area of an Equilateral Triangle

For Teachers 9th - 10th Standards
This task examines how to calculate the area of an equilateral triangle two ways: using triangle congruence and using trigonometric ratios. Aligns with G-CO.C.10 and G-SRT.C.
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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.
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Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: g.co Reflections and Isosceles Triangles

For Teachers 9th - 10th Standards
This task has young scholars 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...
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Handout
Oswego City School District

Regents Exam Prep Center: Theorems and Postulates for Geometry

For Students 9th - 10th Standards
Here is a partial list of theorems, postulates, and properties.

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