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Activity
Texas Instruments

Texas Instruments: Measuring Angles in a Triangle

For Teachers 9th - 10th Standards
In this activity, students learn about the sum of the angles in a triangle. They understand triangles and their interior angles.
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Interactive
Mangahigh

Mangahigh: Shape: Proof of the Sum of the Angles in a Triangle

For Students 9th - 10th Standards
Determine that all angles in a triangle equal 180 degrees.
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Activity
Texas Instruments

Texas Instruments: Betweenness and the Sum of Parts

For Teachers 9th - 10th
In this activity, students will explore the concepts of betweenness and the sum of parts visually, geometrically, and numerically for segments and angles using the Cabri Jr. application. They will investigate how the sum of parts equals...
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Activity
Texas Instruments

Texas Instruments: Triangle Sum

For Teachers 9th - 10th Standards
This activity is used to discover that the sum of the measures of the triangle angles is constant and to discover ways of proving the theorem listed in the activity.
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Interactive
Mangahigh

Mangahigh: Shape: The Angles Inside a Quadrilateral

For Students 5th - 8th Standards
Test your knowledge of the sum of angles inside a quadrilateral.
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Interactive
Mangahigh

Mangahigh: Shape: Interior Angles of Polygons

For Students 9th - 10th
Determine the sum of the interior angles of polygons.
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Unit Plan
Mathigon

Mathigon: Geometry: Angles and Polygons: Drawing Triangles

For Students 9th - 10th Standards
This lesson focuses on the Triangle Inequality, when the sum of the lengths of any two sides of a triangle is greater than the length of the third. When this happens, the three sides cannot form a triangle.
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Handout
Oswego City School District

Regents Exam Prep Center: Exterior Angles of Polygons

For Students 6th - 8th
This site explains what the measure of the sum of exterior angles is for any polygon, and shows how to find the measure of individual exterior angles for regular polygons with a drawn example.
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Unit Plan
Texas Education Agency

Texas Gateway: Making Conjectures About Other Polygons

For Students 9th - 10th
Given information about the properties of polygons, students will verify theorems about the relationships, including the sum of interior angles, and apply these relationships to solve problems.
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Activity
Math Is Fun

Math Is Fun: Triangles Contain 180 Degrees

For Students 9th - 10th Standards
Students learn about the angle-sum theorem. A definition, example, and proof are included.
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PPT
Sophia Learning

Sophia: Using Triangles to Find the Sum of Interior Angles: Lesson 1

For Students 9th - 10th
This lesson demonstrates how to use triangles to determine the sum of the interior angles of a polygon. It is 1 of 5 in the series titled "Using Triangles to Find the Sum of Interior Angles."
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PPT
Sophia Learning

Sophia: Triangle Interior Angles Practice: Lesson 5

For Students 9th - 10th
This lesson provides practice problems that involve the sum of the interior angles of triangles. It is 5 of 6 in the series titled "Triangle Interior Angles Practice."
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PPT
Sophia Learning

Sophia: Triangle Interior Angles Practice: Lesson 1

For Students 9th - 10th
This lesson provides practice problems that involve the sum of the interior angles of triangles. It is 1 of 6 in the series titled "Triangle Interior Angles Practice."
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Activity
Windstream

Ojk's Precalculus Study Page: Double and Half Angle Formulas

For Students 9th - 10th Standards
This tutorial introduces the double-angle and half-angle formulas for sine, cosine, and tangent, and gives sample application and proof exercises. Assumes knowledge of the sum and difference formulas.
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Interactive
University of Colorado

University of Colorado: Ph Et Interactive Simulations: Vector Addition

For Students 9th - 10th Standards
Learn how to add vectors. Drag vectors onto a graph, change their length and angle, and sum them together. The magnitude, angle, and components of each vector can be displayed in several formats.
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Interactive
University of Colorado

University of Colorado: Ph Et Interactive Simulations: Vector Addition

For Students 9th - 10th Standards
Learn how to add vectors. Drag vectors onto a graph, change their length and angle, and sum them together. The magnitude, angle, and components of each vector can be displayed in several formats.
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Interactive
Calculator Soup

Calculator Soup: Triangle Theorems Calculator

For Students 9th - 10th Standards
Each calculation option has sub-bullets that list the sequence of methods used in this calculator to solve for unknown angle and side values including Sum of Angles in a Triangle, Law of Sines, and Law of Cosines.
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Unit Plan
Cuemath

Cuemath: Obtuse Triangle

For Students 9th - 10th Standards
In this mini-lesson, learn about obtuse triangles including the obtuse triangle definition, sides, properties, examples, and other fun facts related to it.
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Unit Plan
Cuemath

Cuemath: Triangles

For Students 5th - 8th Standards
Explore everything about triangles. Learn about the different types, important properties, and how to find its area and perimeter. Check out the solved examples and interactive questions for better understanding.
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Activity
National Council of Teachers of Mathematics

The Math Forum: Problems Library Geometry Triangles

For Students 9th - 10th Standards
This site contains a wealth of problems that deal with the basic definitions of medians, altitudes, angle bisectors, and perpendicular bisectors or the defining characteristics of the different types of triangles. There are also...
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Activity
Texas Instruments

Texas Instruments: Properties of the Centers of a Triangle

For Teachers 9th - 10th
Students investigate the sum of the measures of the interior angles of a triangle. This activity explores interior angles, and their relationship with the exterior angles of a triangle [Requires Adobe Reader.]
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Handout
Other

Sierra College: Trigonometric Identities

For Students 9th - 10th Standards
Provides trigonometric identities, which include fundamental identities, even-odd identities, addition formulas, double-angle formulas, subtraction formulas, product-sum formulas, and identities for sin squared and cos squared.
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Activity
Other

Brown Math: Remembering Trig Identities

For Students 9th - 10th Standards
Faced with a large number of trigonometric identities, students tend to try to memorize them all. This site the emphasis is on understanding how the functions work and on memorizing only about a half dozen of them - all the others work...
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Whiteboard
ClassFlow

Class Flow: Investigating Regular Polygons

For Teachers 9th - 10th
[Free Registration/Login Required] In this lesson students are introduced to regular polygons. Students learn how to find the drawing angle of any given polygon, exterior angle, interior angle and the sum of the angles for a regular...

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