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Lesson Plan
Curated OER

Indirect Proof and Inequalities in one Triangle

For Teachers 10th
For this geometry worksheet, 10th graders complete an indirect proof and order the sides or angles of a triangle. Also, students determine if a triangle can have sides with the given lengths. The two page worksheet contains twelve...
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Instructional Video3:40
CK-12 Foundation

Indirect Proofs in Algebra and Geometry: Lesson

For Students 7th - 12th
Indirectly, it is a good proof method. A segment of a playlist on geometry introduces a way to prove geometric and algebraic statements. Using a general examples, the video shows how to develop an indirect proof.
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Lesson Plan
Curated OER

Indirect Proof and Inequalities in One Triangle

For Teachers 10th
In this geometry worksheet, 10th graders order the sides and angles of a triangle and determine the range of the third side of a triangle given the lengths of two sides.  The one page worksheet contains sixteen questions.  Answers are...
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Activity
Education Development Center

Sum of Rational and Irrational is Irrational

For Teachers 8th - 9th Standards
Sometimes the indirect path is best. Scholars determine whether the sum of a rational number and an irrational number is irrational. Reading a transcript of a conversation between classmates leads to an indirect proof of this concept.
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Lesson Plan
Curated OER

Conditional Statements

For Teachers 9th - 12th
Learners are introduced to the topic of proofs in Geometry. During a PowerPoint presentation, they take notes on indirect proofs and have groups of students write a true statement. They are assessed on the statement and how well they...
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Lesson Plan
Curated OER

Special Segments in a Triangle

For Teachers 10th
In this geometry worksheet, 10th graders review the vocabulary associated with the special segments of a triangle and the associated points of concurrency and solve problems in which they find the indicated missing angle or segment.  The...
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Worksheet
Curated OER

Properties of Geometry

For Students 10th
In this properties of geometry worksheet, 10th graders solve and complete 12 different problems that include various theorems. First, they draw a figure that illustrates the SAS inequality property. Then, students prove that two line...
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Unit Plan
CK-12 Foundation

Ck 12: Geometry: Indirect Proof in Algebra and Geometry

For Students 9th - 10th Standards
[Free Registration/Login may be required to access all resource tools.] This concept teaches students how to write an indirect proof and provides examples of indirect proofs in Algebra and Geometry.
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Unit Plan
CK-12 Foundation

Ck 12: Geometry: Indirect Proof in Algebra and Geometry

For Students 9th - 10th Standards
[Free Registration/Login may be required to access all resource tools.] Write algebraic and geometric indirect proofs.
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Primary
Kent State University

Kent State University: Indirect Proofs, Michael Byron

For Students 9th - 10th
Use this site to explore an excellent discussion of indirect proofs. The site explains in detail why such a method works as a proof and gives steps to obtain such a proof.
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Activity
Oswego City School District

Regents Exam Prep Center: Indirect Euclidean Proofs

For Students 9th - 10th
This Oswego City School District Regents Exam Prep site shows you how to proof something by showing that it is false. This look at indirect proofs includes a practice and a teacher resource page, which features a warm-up activity.
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Unit Plan
University of Saskatchewan (Canada)

University of Saskatchewan: Techniques for Proofs

For Students 9th - 10th
The University of Saskatchewan's Department of Mathematics and Statistics provides high school students with online tutorials and exercises on what they deem some of the most important techniques for mathematical proofs: truth tables,...
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Handout
CK-12 Foundation

Ck 12: Geometry: Proofs Study Guide

For Students 9th - 10th Standards
[Free Registration/Login may be required to access all resource tools.] This study guide reviews proofs: algebraic proof, properties of congruence, and geometric proofs (two-column).
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Handout
CK-12 Foundation

Ck 12: Geometry: Types of Reasoning Study Guide

For Students 9th - 10th Standards
[Free Registration/Login may be required to access all resource tools.] Reasoning is a fundamental part of geometric proofs. There are several types of reasoning, many of which we innately and naturally picked up. However, the different...
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Activity
University of Cambridge

University of Cambridge: Nrich: Code Breaker

For Students 3rd - 8th
Do your logic skills need sharpening? Use the interactive code breaker to at this one page website to do just that! The solution is available to double check your solution.

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