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Lesson Plan
Curated OER

The Pythagorean Theorem and Classifying Triangles

For Teachers 9th - 12th Standards
Through the examination of the relationship between the lengths of the sides of a triangles high schoolers will learn the classification of triangles (acute, right, or obtuse).
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Lesson Plan
Curated OER

Basic Right Triangles

For Teachers 2nd - 4th
Elementary schoolers examine the attributes of triangles. In this triangle lesson, learners compare regular triangles and right triangles. They explore vertices and angles and investigate obtuse and acute angles. Pupils draw multiple...
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Lesson Plan
Curated OER

Exploring Polygons and The Greedy Triangle

For Teachers 1st - 3rd
Excellent lesson! Anne Linehane's geometry story, The Greedy Triangle, offers an opportunity to practice forming various types of polygons with your learners. Using elastic bands (or Chinese jump ropes), partners form the various shapes...
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Worksheet
Curated OER

Solving Problems with Angles

For Students 4th - 6th
Upper elementary math whizzes complete word problems having to do with measurements of angles. They complete 10 multiple choice problems.
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Lesson Plan
Alabama Learning Exchange

Triangle Congruence with Rigid Motion

For Students 9th - 12th Standards
Combine transformations and triangle congruence in a single lesson. Scholars learn to view congruent triangles as a rigid transformation. Using triangle congruence criteria, learners identify congruent triangles and the rigid...
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Interactive
Shodor Education Foundation

Squaring the Triangle

For Students 8th - 12th Standards
Teach budding mathematicians how to square a triangle with an interactive that shows a graphical proof of the Pythagorean Theorem. Pupils alter the lengths of the legs using sliders. Using the inputted lengths, the applet displays the...
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Lesson Plan
Curated OER

Exterior and Interior Angles of Triangles

For Teachers 10th
Tenth graders explore the exterior and interior angles of triangles. They use a theorem in order to prove a theorem about all polygons. Students use the theorem and its applications to find the angles of different types of triangles.
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Lesson Plan
Curated OER

Obtuse Angles

For Teachers 3rd
Third graders recognize and identify geometric shapes, work with manipulatives to reinforce understanding, and create polygons with various angles to display their knowledge of the different types of angles.
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Worksheet
Curated OER

Types of Triangles

For Students 2nd - 4th
Young math whizzes solve four problems in which a triangle with labeled angle measurements is analyzed. They mark if each triangle is acute, right, or obtuse.
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Worksheet
Mt. San Antonio Collage

Inequalities in a Triangle

For Students 9th - 12th Standards
Stuck with triangle proofs? Take a 180° and provide learners with a guided worksheet that tests their knowledge with triangle inequalities. The questions require different types of proofs that range in levels of difficulty. 
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Lesson Plan
National Security Agency

Classifying Triangles

For Teachers 4th - 8th Standards
Building on young mathematicians' prior knowledge of three-sided shapes, this lesson series explores the defining characteristics of different types of triangles. Starting with a shared reading of the children's book The Greedy Triangle,...
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Worksheet
Curated OER

Triangles

For Students 10th
In this triangles activity, 10th graders solve 12 different problems that include various angles of triangles. First, they determine the measure of an exterior angle. Then, students determine the measure of any of the base angles of an...
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Lesson Plan
Curated OER

Angles in Triangles

For Teachers 8th
Eighth graders translate word problems using mathematical ideas. In this geometry lesson, 8th graders identify angles of triangles using equations and the triangle sum theorem. They create angles with a protractor and straight edge.
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Worksheet
Curated OER

Learning About Triangles

For Students 4th - 6th
Upper graders label four triangles and fill in the labels correctly. They draw three original triangles and answer the questions about them.
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Worksheet
Curated OER

Constructions and Angles

For Students 6th - 10th
In this triangle constructing and classifying worksheet, students read through a tutorial on triangles and angles. Then, students complete 17 exercises in which they answer questions about angles and triangles. By clicking on the "Check"...
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Worksheet
Curated OER

Triangles

For Students 10th
In this triangles worksheet, 10th graders solve and complete 22 different problems related to various types of triangles. First, they name the shortest and longest sides and the smallest and largest angles in each of triangles...
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Lesson Plan
Curated OER

Special Right Triangles

For Teachers 9th - 12th Standards
Using the Pythagorean Theorem to solve for missing angles, young scholars evaluate right triangles and their properties.
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Worksheet
Curated OER

Countdown Challenge: Triangle Inequality Theorem

For Students 7th - 8th
In this triangle inequality activity, students test the Triangle Inequality Theorem. They measure the sides of given triangles, identify the type of triangle, and name angles in the triangle. The one-page activity contains 36 problems.
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PPT
Primary Resources

Different Types of Triangles

For Teachers 4th - 5th Standards
Are there different types of triangles? Yes there are, and this presentation describes each by its properties or characteristics. Right, equilateral, isosceles, and scalene are all shown and defined. The presentation isn't particularly...
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Lesson Plan
Curated OER

Ratios in Right Triangles

For Teachers 9th - 12th Standards
Learners calculate the sides of right triangles in this trigonometric ratios lesson. They use Cabri Jr. software and TI-83 or TI-84 calculators to find the side lengths and their ratios to each other for various triangles. The provided...
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Lesson Plan
EngageNY

Similar Triangles in Circle-Secant (or Circle-Secant-Tangent) Diagrams

For Teachers 9th - 12th Standards
First angle measures, now segment lengths. High schoolers first measure segments formed by secants that intersect interior to a circle, secants that intersect exterior to a circle, and a secant and a tangent that intersect exterior to a...
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Printables
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K-5 Math Teaching Resources

2-D Shape Cards

For Students K - 5th Standards
Add some visual support to your elementary geometry lessons with this set of printable shape cards. From triangles and squares to octagons and nanogons, this simple resource can be used in countless ways to develop children's knowledge...
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Assessment
Mathed Up!

Angles

For Students 6th - 8th Standards
What does a geometric farmer drive? A protractor, of course! A set of assessment worksheets prompts learners to use a protractor as they measure angles, name angles, and identify lines. Use the video as a way to introduce the concepts. 
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Assessment
Bowland

Rods and Triangles

For Teachers 6th - 9th
Scholars explore triangles with rods of different lengths. Using rods of 2, 4, 6, 8, and 10 cm class members build as many different types of triangles as they can. They also describe properties of these triangles and determine...