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Interactive
Scholastic

Study Jams! Area of a Triangle

For Students 4th - 6th Standards
Even though there is a wide variety of different triangles in the world, knowing a single equation allows us to find the area of each and every one of them. Follow along with this step-by-step presentation as Zoe clearly models how to...
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Lesson Plan
EngageNY

Congruence Criteria for Triangles—AAS and HL

For Students 9th - 10th Standards
How can you prove it? Guide classes through an exploration of two possible triangle congruence criteria: AAS and HL. Learners connect this criteria to those previous learned and also explore criteria that does not work. The lesson...
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Instructional Video4:47
Corbett Maths

Construct a 30 Degree Angle

For Students 8th - 11th Standards
Split it down the middle. Using the tools of geometric construction, the video shows two different methods of constructing a 30-degree angle. The first method bisects an angle of an equilateral triangle. The second uses the diagonal of a...
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Assessment9:45
Mathed Up!

Angles in Polygons

For Students 8th - 10th Standards
Show your class that finding angle measures is a regular calculation with a resource that provides 12 problems dealing with the measures of angles in regular polygons. Pupils use formulas for the sum of measures of angles in a polygon to...
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Interactive
CK-12 Foundation

Pythagorean Theorem for Solving Right Triangles: Solving the Triangle

For Students 9th - 12th Standards
Observe the change in the trigonometric ratios as angles vary. An interactive provides the values of trigonometric ratios for both acute angles in a right triangle. Pupils create a right triangle to match given criteria and find the...
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Assessment6:43
Mathed Up!

Angles in Triangles and Quadrilaterals

For Students 8th - 10th Standards
This short video show viewers how to connect the sum of the angles in a triangle to other angle measurements. Pupils determine the missing measures for angles involved with triangles and quadrilaterals. Class members then must explain...
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Instructional Video2:22
Corbett Maths

Constructing ASA Triangles

For Students 8th - 11th Standards
The narrator of a short video explains the steps in constructing a triangle given the measure of two angles and the length of the side between the angles. The resource provides opportunities for pupils to practice the skill with two...
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Unit Plan
Virginia Department of Education

Classifying Angles

For Teachers 4th - 8th Standards
Don't be obtuse, this geometry unit is the just the right resource for educating the acute young minds in your class. From classifying and measuring angles, to determining the congruence of shapes, this resource covers a wide range of...
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Handout
Charleston School District

Similar Triangles

For Students 8th Standards
Are they similar? The lesson provides an explanation of the angle-angle criterion for triangle similarity. Several problems allow the class to determine whether the two triangles with the given angle measures are similar or not. 
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Lesson Plan
Illustrative Mathematics

Sum of Angles in a Polygon

For Teachers 8th - 12th Standards
How can learners use algebra to solve a geometry problem? Help learners create an equation that shows the relationship between the number of sides of a polygon and the sum of the interior angles. Students are asked to divide the...
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Handout
Charleston School District

Parallel Lines Cut by a Transversal

For Students 8th Standards
Pupils study angle measurements between different types of angles associated with parallel lines and transversals. The independent practice asks pupils to identify the types of angles in a diagram and to determine the measure of angles. 
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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 activity series explores the defining characteristics of different types of triangles. Starting with a shared reading of the children's book The Greedy...
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Unit Plan
1
1
Mathematics Vision Project

Similarity and Right Triangle Trigonometry

For Teachers 10th - 12th Standards
Starting with similar triangles and dilation factors, this unit quickly and thoroughly progresses into the world of right triangle features and trigonometric relationships. Presented in easy-to-attack modules with copious application...
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Workbook
1
1
University of Utah

Geometry: Angles, Triangles, and Distance

For Students 8th Standards
The Pythagorean Theorem is a staple of middle school geometry. Scholars first investigate angle relationships, both in triangles and in parallel lines with a transversal, before proving and applying the Pythagorean Theorem.
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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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Lesson Plan
EngageNY

More About Similar Triangles

For Teachers 8th Standards
Determine whether two triangles are similar. The lesson presents opportunities for pupils to find the criterion needed to show that two triangles are similar. Scholars use the definition of similarity to find any missing side...
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Interactive
CK-12 Foundation

Angles of Elevation and Depression: Fly-By Calibration

For Students 9th - 12th Standards
Determine the distance between two trees from afar. Pupils use an interactive resource to create two right triangles using trees and a plane. They determine the horizontal legs of each triangle to find the distance between the two trees.
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Instructional Video1:47
Corbett Maths

Constructing SAS Triangles

For Students 8th - 11th Standards
Two sides and an angle ... a triangle it makes. Given the measure to two sides and the angle between them, the narrator of a short video shows how to draw a triangle with a ruler and protractor. Pupils use handouts to practice the newly...
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Lesson Plan
Willow Tree

Angle Sum Property of Triangles

For Students 8th - 11th Standards
All triangles have some things in common. Using these properties of triangles, learners find missing angle measures. Scholars use the Angle Sum Property and properties of special triangles throughout the lesson.
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Lesson Plan
Willow Tree

Interior Angles, Exterior Angles, and Diagonals of Polygons

For Students 8th - 11th Standards
How does the number of sides of a polygon affect the angle measures? Learners recognize a pattern in finding the total measure of interior and exterior angles and the number of diagonals. They use the patterns to calculate the number of...
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Interactive
CK-12 Foundation

Angle-Side-Angle Triangles: Caution Tape

For Students 10th - 12th Standards
Don't lose your marbles. Scholars use an interactive to create a triangle that closes off a portion of a sidewalk with loose marbles. The Law of Sines helps them find the side measures of such a triangle.
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Unit Plan
Mathematics Vision Project

Geometric Figures

For Teachers 10th - 12th Standards
Logical thinking is at the forefront of this jam-packed lesson, with young mathematicians not only investigating geometric concepts but also how they "know what they know". Through each activity and worksheet, learners wrestle with...
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Lesson Plan
EngageNY

Informal Proof of AA Criterion for Similarity

For Teachers 8th Standards
What does it take to show two triangles are similar? The 11th segment in a series of 16 introduces the AA Criterion for Similarity. A discussion provides an informal proof of the theorem. Exercises and problems require scholars to apply...
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Interactive
CK-12 Foundation

Unit Circle: Medieval Castle Defense

For Students 10th - 12th Standards
Who needs a plan — let trigonometry protect you! Pupils determine the angle of an approaching enemy to a village wall. The scholars determine the exact value of trigonometric functions for the angle. Class members use trigonometry to...