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Instructional Video22:15
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Flipped Math

Intro to Proofs

For Students 9th - 12th Standards
Prove the best way to keep up in Geometry. Scholars first review algebraic properties from Algebra. Learners then use the properties to create two-column proofs to solve linear equations before completing algebraic proofs by providing...
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Worksheet
Curated OER

Geometry: Properties of Triangles

For Students 10th - 12th
In this properties of triangles worksheet, learners use their knowledge of triangles to find determine angle measurement. They use geometric theorems to prove equal angles. This three-page worksheet contains 15 multi-step geometry...
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Lesson Plan
2
2
Illustrative Mathematics

Shortest Line Segment from a Point P to a Line L

For Teachers 9th - 11th Standards
One of the hardest skills for many young geometers to grasp is to move beyond just declaring obvious things true, and really returning to fundamental principles for proof. This brief exercise stretches those proving muscles as the class...
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Lesson Plan
Curated OER

TI Workshop Presentation Guide for "Preparing for Proofs"

For Teachers 9th - 12th Standards
Pupils discover proofs using the TI in this geometry lesson. They collect data from newspaper and magazines and analyze their data using the TI, relating it to proofs.
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Lesson Plan
EngageNY

Unknown Angle Proofs—Writing Proofs

For Teachers 9th - 10th Standards
What do Sherlock Holmes and geometry have in common? Why, it is a matter of deductive reasoning as the class learns how to justify each step of a problem. Pupils then present a known fact to ensure that their decision is correct.
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Lesson Plan
EngageNY

Circles, Chords, Diameters, and Their Relationships

For Teachers 9th - 10th Standards
A diameter is the longest chord possible, but that's not the only relationship between chords and diameters! Young geometry pupils construct perpendicular bisectors of chords to develop a conjecture about the relationships between chords...
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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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Workbook
1
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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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Worksheet
Curated OER

Geometric Proof and Angles

For Students 10th
In this geometry worksheet, 10th graders write two-column and paragraph proofs to prove angle pair relationships.  The one page worksheet contains five problems.  Answers are not included. 
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Worksheet
Curated OER

Proofs Chapter 2: Geometry

For Students 10th - 11th
In this geometry learning exercise, learners look at given pictures and prove congruent lines and angles. This three-page learning exercise contains nine multi-step problems.
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Worksheet
Curated OER

Identify Similar Triangles With Proofs

For Students 10th - 12th
In this similar triangle worksheet, students write a two-column proof to explain why determined triangles are similar. Given some line lengths and angle measurements, students use proofs to identify the ratio of specified angles. This...
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Lesson Plan
Curated OER

Logic and Proof Writing

For Teachers 9th - 10th
Students define inductive and deductive reasoning and write two column proofs. In this geometry lesson, students analyze arguments and draw conclusion. They define steps necessary to arrive at the correct answer when completing proofs.
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Assessment
Math Worksheets Center

Congruent Triangle Proofs Quiz

For Students 9th - 12th
A congruent triangles quiz challenges teenage mathematicians to complete a pair of geometric proofs. Each problem includes a picture of the triangles in question, a given set of information, and the five steps needed to finish the proof....
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Worksheet
Curated OER

Quiz: Direct Euclidean Proofs

For Students 10th - 12th
In this Euclidean proof activity, students observe models and read given proofs. Students determine conclusions based upon the given information. This one-page activity contains ten Euclidean proof problems.
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Worksheet
Curated OER

Proofs in Coordinate Geometry

For Students 10th - 11th
In this coordinate geometry worksheet, students identify the lengths of a quadrilateral and find the slope of a line. They use proofs to identify the characteristics of given quadrilaterals. This one-page worksheet contains ten problems.
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Worksheet
Curated OER

Pre-Proof Warm-Ups

For Students 10th
In this pre-proofs learning exercise, 10th graders solve and complete 10 different problems that include various proofs and their definitions. They use the diagram shown and the given information to write the direct conclusion for each...
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Lesson Plan
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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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Worksheet
Curated OER

Using Proof in Algebra

For Students 10th
In this using proofs in algebra worksheet, 10th graders solve 2 proofs by applying the many rules from algebra for the Properties of Equality for real numbers. They name the property that justifies each statement as seen in the...
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Worksheet
Curated OER

Proofs: Solving Equations

For Students 9th - 12th
In this proofs worksheet, high schoolers solve 4 short answer problems. Students identify the correct reason for each step in solving each multi-step equation.
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Lesson Plan
Curated OER

Getting It Right! An Investigation of the Pythagorean Theorem

For Teachers 6th - 8th
Learners construct a variety of right triangles using a right-angled set square, cutting corners from pieces of paper or cardboard, and using dynamic geometry software. They measure the sides of these various right triangles and record...
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Instructional Video11:57
2
2
Flipped Math

Side Splitter Theorem

For Students 9th - 12th Standards
Apply perspective to similarity. Individuals learn about the Side Splitter Theorem by looking at perspective drawings. Pupils use the theorem and its corollary to find missing lengths in figures. Next, they practice using the theorem and...
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Lesson Plan
EngageNY

Congruence Criteria for Triangles—ASA and SSS

For Students 9th - 10th Standards
How do you know if a pair of triangles are congruent? Use the lesson to help class members become comfortable identifying the congruence criteria. They begin with an exploration of ASA and SSS criteria through transformations and...
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Lesson Plan
EngageNY

Special Lines in Triangles (part 2)

For Teachers 9th - 10th Standards
Medians, midsegments, altitudes, oh my! Pupils study the properties of the median of a triangle, initially examining a proof utilizing midsegments to determine the length ratio of a median. They then use the information to find missing...
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Lesson Plan
EngageNY

Congruence Criteria for Triangles—SAS

For Students 9th - 10th Standards
Looking for a different approach to triangle congruence criteria? Employ transformations to determine congruent triangles. Learners list the transformations required to map one triangle to the next. They learn to identify congruence if...

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