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Assessment
Inside Mathematics

Circles in Triangles

For Teachers 9th - 12th Standards
Challenge the class with inscribed circles in triangles. The assessment task requests class members use their knowledge of circles and right triangles to prove two triangles are congruent. They go on to utilize their knowledge of...
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Lesson Plan
Virginia Department of Education

Similar Triangles

For Teachers 9th - 11th Standards
Pupils work in pairs to investigate what it takes to prove that two triangles are similar. They work through various shortcuts to find which are enough to show a similarity relationship between the triangles. Small groups work with the...
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Lesson Plan
EngageNY

Base Angles of Isosceles Triangles

For Students 9th - 10th Standards
Build confidence in proofs by proving a known property. Pupils explore two approaches to proving base angles of isosceles triangles are congruent: transformations and SAS. They then apply their understanding of the proof to more complex...
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Worksheet
Mt. San Antonio Collage

Isosceles Triangles and Special Line Segments

For Students 9th - 12th Standards
Under which conditions can a triangle be classified as isosceles? High schoolers practice identifying isosceles triangles and special line segments, including angle bisectors, medians of triangles, and perpendicular bisectors of sides of...
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Lesson Plan
West Contra Costa Unified School District

Investigating Similar Triangles

For Teachers 9th - 12th
Let your use of the resource be in proportion to its usefulness. Pupils investigate similar triangles by measuring side lengths and considering given angle measures. The results of the investigation help develop generalizations about...
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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
Curated OER

Congruent Triangles

For Teachers 10th
Tenth graders explore congruent triangles.  In this geometry lesson, 10th graders investigate the conditions necessary to prove two triangles are congruent by SSS, ASA, AAS, or SAS. 
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Worksheet
Curated OER

Exploring Congruent Triangles

For Students 10th
For this congruent triangles worksheet, 10th graders solve 10 different problems related to exploring various types of congruent triangles. First, they label the corresponding parts and use the figures to complete each statement. Then,...
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Lesson Plan
EngageNY

Applications of Congruence in Terms of Rigid Motions

For Students 9th - 10th Standards
Corresponding parts, congruent parts, congruent corresponding parts—what does it all mean? The resource challenges pupils to identify corresponding parts for pairs of figures. It uses examples of figures that undergo rigid...
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Lesson Plan
West Contra Costa Unified School District

Congruent and Similar Polygons

For Teachers 9th - 12th
What's similar about congruent and similar polygons? Young mathematicians first measure the side lengths and angles of given figures. They use these measurements to determine relationships between side lengths and angles of congruent and...
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Lesson Plan
EngageNY

Definition of Congruence and Some Basic Properties

For Students 8th Standards
Build a definition of congruence from an understanding of rigid transformations. The lesson asks pupils to explain congruence through a series of transformations. Properties of congruence emerge as they make comparisons to these...
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Worksheet
2
2
K12 Reader

Congruent Geometric Shapes

For Students 2nd - 3rd Standards
Here's a reading comprehension worksheet that focuses on congruent geometric shapes. After reading a short article about congruent figures, kids respond to a series of comprehension questions.
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Assessment
Concord Consortium

Isosceles Triangle Spaces

For Students 7th - 10th Standards
How many different types of triangles can your class name? A discovery lesson guides learners through an exploration of the different triangle types and the relationships between their angles and sides. Using coordinate geometry,...
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Lesson Plan
1
1
Illustrative Mathematics

Similar Triangles

For Teachers 9th - 11th Standards
Proving triangles are similar is often an exercise in applying one of the many theorems young geometers memorize, like the AA similarity criteria. But proving that the criteria themselves are valid from basic principles is a great...
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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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Lesson Plan
Illustrative Mathematics

Joining Two Midpoints of Sides of a Triangle

For Teachers 9th - 11th Standards
Without ever using the actual term, this exercise has the learner develop the key properties of the midsegment of a triangle. This task leads the class to discover a proof of similar triangles using the properties of parallel lines cut...
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Worksheet
Curated OER

More Congruent Triangles

For Students 10th
In this congruent triangles worksheet, 10th graders solve 5 various types of geometry problems related to triangles. First, they draw and label triangles, indicating the additional pairs of corresponding parts that would have to be...
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Worksheet
Curated OER

Congruent Triangles

For Students 10th
In this congruent triangles learning exercise, 10th graders solve and complete 10 different problems that involve various congruent triangles. First, they determine the length of the third side given the other two. Then, students...
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Worksheet
Curated OER

Quiz: Beginning Congruent Triangle Proofs

For Students 10th - 11th
In this congruent triangle proof activity, students write theorems to prove the congruence of given triangles. This one-page activity contains three given polygons to prove congruence.
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Interactive
Curated OER

Similar Triangles Multiple Choice

For Students 8th - 10th
In this triangle relationships worksheet, students identify measurements in similar and congruent triangles. Each problem features a drawing of two or more triangles. Students identify missing measurements. There are 5 multiple choice...
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Worksheet
Curated OER

Proofs

For Students 8th - 11th
In this geometric proof worksheet, students compose 20 triangle congruency proofs. Students will decide if there is enough information in problems 1-6 to prove if any triangles are congruent. In problems 17 to 20, students use given...
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Unit Plan
1
1
EngageNY

Congruence, Proof, and Constructions

For Teachers 8th - 10th Standards
This amazingly extensive unit covers a wealth of geometric ground, ranging from constructions to angle properties, triangle theorems, rigid transformations, and fundamentals of formal proofs.  Each of the almost-forty lessons is broken...
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Lesson Plan
Curated OER

Triangle Proofs

For Teachers 10th
Tenth graders complete a unit of lessons on congruent triangles and triangle proofs. They observe and participate in teacher-led discussions of examples of the methods to prove that triangles are congruent, and create an original proof.
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Lesson Plan
EngageNY

Properties of Parallelograms

For Teachers 9th - 10th Standards
Everyone knows that opposite sides of a parallelogram are congruent, but can you prove it? Challenge pupils to use triangle congruence to prove properties of quadrilaterals. Learners complete formal two-column proofs before moving on to...

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