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Assessment
Mathematics Assessment Project

Circles in Triangles

For Students 9th - 12th Standards
Circles, and triangles, and tangents, oh my! In the assessment task, learners first answer questions leading to the radius of an inscribed circle for a given right triangle. They then use the result to independently determine the radius...
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Lesson Plan
Alabama Learning Exchange

Triangle Area: No Height? Use the Sine

For Students 9th - 12th Standards
No height? No problem! Learners use their knowledge and a little help from GeoGebra to develop the Law of Sines formula. The Law of Sines helps to determine the height of triangles to calculate the area.
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Activity
Education Development Center

Similar Triangles

For Students 8th - 10th Standards
Model geometric concepts through a hands-on approach. Learners apply similar triangle relationships to solve for an unknown side length. Before they find the solution, they describe the transformation to help identify corresponding sides.
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Lesson Plan
Mathematics Assessment Project

Inscribing and Circumscribing Right Triangles

For Teachers 9th - 12th Standards
High schoolers attempt an assessment task requiring them to find the radii of inscribed and circumscribed circles of a right triangle with given dimensions. They then evaluate provided sample responses to consider how to improve their...
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Lesson Plan
EngageNY

Triangle Congruency Proofs (part 1)

For Teachers 9th - 10th Standards
Can they put it all together? Ninth graders apply what they know about proofs and triangle congruence to complete these proofs. These proofs go beyond the basic triangle congruence proofs and use various properties, theorems, and...
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Lesson Plan
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Illustrative Mathematics

Equal Area Triangles on the Same Base II

For Teachers 9th - 12th Standards
A deceptively simple question setup leads to a number of attack methods and a surprisingly sophisticated solution set in this open-ended problem. Young geometers of different strengths can go about defining the solutions graphically,...
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Lesson Plan
West Contra Costa Unified School District

Investigating Special Right Triangles

For Teachers 9th - 12th
Scholars first investigate relationships in the side lengths of 30°-60°-90° triangles and 45°-45°-90° triangles. This knowledge then helps them solve problems later in the lesson about special right triangles.
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Lesson Plan
EngageNY

Construct an Equilateral Triangle (part 1)

For Teachers 9th - 10th Standards
Drawing circles isn't the only thing compasses are good for. In this first installment of a 36-part series, high schoolers learn how to draw equilateral triangles by investigating real-world situations, such as finding the location of a...
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Lesson Plan
EngageNY

Special Triangles and the Unit Circle

For Teachers 11th - 12th Standards
Calculate exact trigonometric values using the angles of special right triangles. Beginning with a review of the unit circle and trigonometric functions, class members use their knowledge of special right triangles to find the value of...
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Assessment
Illustrative Mathematics

Coordinates of Equilateral Triangles

For Students 9th - 12th Standards
Can it be constructed? The task poses the question whether it is possible to have an equilateral triangle with its vertices located at integer coordinates. Pupils work with their knowledge of trigonometric ratios and the Pythagorean...
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Assessment
CPALMS

2D Rotations of Triangles

For Students 9th - 12th Standards
Where does the line of rotation need to be to get a cone? Pupils respond to three questions involving rotating a right triangle about different lines. The scholars describe the solid created along with providing details about its...
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Assessment
Concord Consortium

In a Triangle

For Students 9th - 12th Standards
What's in a triangle? Just 180 degrees worth of angles! Young learners use given angle relationships in a triangle to write an algebraic representation. Using a system of equations, they simplify the equation to a linear representation.
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Interactive
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GeoGebra

Triangle Dilations

For Students 9th - 12th Standards
Stretch the class' knowledge of dilations. With the aid of the rubber band stretcher tool, learners perform dilations. They dilate the triangle by a whole number scale and a fractional scale from two centers of dilation.
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Worksheet
Curated OER

Triangles

For Students 10th
In this triangles worksheet, 10th graders solve 3 extensive informal geometry problems that involve triangles. First, they sketch a triangle, selecting 3 of the sides and constructing 3 midpoints. Students then draw each of 3 medians by...
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Interactive
Curated OER

Triangle Problems-Base, Height, and Area

For Students 10th
In this geometry worksheet, 10th graders find the base, height, or area of a triangle. The one page interactive worksheet contains ten questions. Answers and hints are included. 
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Worksheet
Curated OER

Learning Triangles

For Students K - 1st
In this triangles worksheet, students recognize triangles. Students complete the worksheet by practicing drawing triangles and recognizing triangles in a picture.
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Lesson Plan
Curated OER

Trigonometric Functions of Acute Right Triangles

For Teachers 9th - 11th
Students derive the six trigonometric functions. In this trigonometry lesson, students show their understanding of trigonometric functions as they relate the right triangles. They find the missing angles and side use trig ratios of sine,...
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Worksheet
Curated OER

Find the Perimeter of Triangles

For Students 5th - 7th
For this perimeter worksheet, students calculate the perimeter of various different triangles. There are four problems to solve.
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Worksheet
Curated OER

Find the Side of the Triangle

For Students 9th - 10th
In this geometry worksheet, students investigate the missing side of  triangles given the other two sides. There are 5 questions with a solution key.
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Lesson Plan
Curated OER

Exploring Characteristics of Triangles

For Teachers 9th - 11th
Young scholars draw triangles and explore the classification of each using the measures of interior angles and lengths of sides. They investigate the sum of the interior angles of various triangles and conjecture and prove the theorem:...
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Worksheet
Curated OER

Classifying Triangles

For Students 6th
In this classifying triangles worksheet, 6th graders write the type of triangle, acute, right or obtuse, for 9 pictures of triangles, answers included.
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Lesson Plan
Curated OER

A Triangle Expansion

For Teachers 9th - 12th
Students review the foil method used to multiply two binomials. In this lesson on evaluating algebraic expressions, students are able to identify the coefficient in an algebraic expression, "act out" the foil method of multiplying...
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Activity
Curated OER

Triangle Series

For Teachers 9th - 12th Standards
Your algebra learners emphasize the"geometric" in geometric series as they use a common ratio between algebraic terms and find that it corresponds to a repeated similarity transformation. 
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Lesson Plan
Curated OER

Circumcenter of a Triangle

For Teachers 9th - 12th Standards
Your geometry learners will discover and show the construction of the circumcenter of a triangle. Guided by the steps in the activity, they construct perpendicular bisectors of each side that have a point of concurrency called the...

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