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Unit Plan
CK-12 Foundation

Ck 12: Geometry: Two Column Proofs Intermediate

For Students 9th - 10th Standards
[Free Registration/Login may be required to access all resource tools.] This concept teaches students how to write two-column proofs, and provides proofs for the Right Angle Theorem, Same Angle Supplements Theorem, and Vertical Angles...
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Unit Plan
CK-12 Foundation

Ck 12: Geometry: Two Column Proofs

For Students 9th - 10th
[Free Registration/Login may be required to access all resource tools.] Write two-column proofs.
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Website
National Council of Teachers of Mathematics

The Math Forum: Ask Dr. Math: Order of a Proof

For Students 9th - 10th Standards
The site gives a diagram of steps to a proof. Dr. Math explains why the step order of a proof is important.
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Website
National Council of Teachers of Mathematics

The Math Forum: Ask Dr. Math: Building Two Column Proofs

For Students 9th - 10th Standards
Use this site to find details of how to construct a two column proof. Dr. Math responds to a question posed by a student and details the reasons for the order of steps and shows two different ways to do the same proof.
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Website
Cut the Knot

Cut the Knot!: Proofs in Mathematics

For Students 9th - 10th Standards
This site provides an explanation of mathematical proofs. It also has links to different types of proofs.
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Lesson Plan
Science Buddies

Science Buddies: Inscribing a Circle in a Triangle Using the Geometry Applet

For Teachers 9th - 10th
Here is a project that combines Computer Science and Mathematics. Prove a method for inscribing a circle within a triangle (as shown). You'll also learn how to create an interactive diagram to illustrate your proof, using an applet that...
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Interactive
Other

Math Court: A Game of Proving Things

For Students 9th - 10th Standards
This site contains a game to help students better learn how to write proofs. The game has several different levels. The game can be played online or cards and board may be printed and used in the classroom.
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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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eBook
CK-12 Foundation

Ck 12: Interactive Geometry: 4.1 Theorems and Proofs

For Students 9th - 10th Standards
Understand theorems and proofs as they relate to geometry.
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Activity
Oswego City School District

Regents Exam Prep Center: Styles of Proof

For Students 9th - 10th Standards
Find out the general form for two column proofs, flow proofs, and paragraph proofs here. The site is very brief and discusses each type of proof using the same example.
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eBook
CK-12 Foundation

Ck 12: Interactive Geometry: 11.1 Descriptions of Events

For Students 9th - 10th Standards
In a coordinate proof, geometric statements using algebra and the coordinate plane.
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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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Interactive
National Council of Teachers of Mathematics

Nctm: Illuminations: Proof Without Words: Completing the Square

For Students 9th - 10th Standards
Use this interactive geometric proof to complete the square using geometry.
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Activity
National Council of Teachers of Mathematics

Nctm: Illuminations: Proof Without Words: Pythagorean Theorem

For Students 9th - 10th Standards
This applet proves the Pythagorean Theorem "without words" using geometry.
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eBook
Mathigon

Mathigon: Euclidean Geometry: Euclid's Axioms

For Students 9th - 10th Standards
This lesson focuses on Euclid's Axioms, simple, intuitive statements, that everyone agrees are true. An axiom(or postulate) is a mathematical statement that is regarded as "self-evident" and accepted without proof. A key part of...
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Website
Other

Propagation of Light Using Geometry

For Students 9th - 10th
A discussion of Christian Huygens' contribution to wave optics, and particularly to our understanding of the reflection and refraction of light. Excellent diagrams and a geometric proof on why the law of reflection is mathematically...
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Activity
Maths Challenge

Maths challenge.net: Tri Angles

For Students 9th - 10th Standards
A geometry proof involving exterior angles of a triangle.
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Unit Plan
CK-12 Foundation

Ck 12: Geometry: Conjectures and Counterexamples

For Students 9th - 10th
[Free Registration/Login may be required to access all resource tools.] In this lesson students make conjectures and provide counterexamples. Students examine guided notes, review guided practice, watch instructional videos and attempt...
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Activity
Varsity Tutors

Varsity Tutors: Hotmath: Practice Problems: Logic and Proof Exercises

For Students 9th - 10th Standards
Twenty-five problems cover the topic of logic and proof in different geometry settings. They are given with each step to the solution cleverly revealed one at a time. You can work each step of the problem then click the "View Solution"...
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Lesson Plan
Texas Instruments

Texas Instruments: Bring Geometry to Life

For Teachers 9th - 10th Standards
In this activity, students use the Geometer's Sketchpad application to construct Euler's Line, Pythagorean Proof, and Fermat's point. They also investigate the concept of perimeter.
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Unknown Type
McGraw Hill

Glencoe Mathematics: Self Check Quiz on Reasoning & Proof

For Students 9th - 10th Standards
The online assessment demonstrates knowledge of concepts utilized in Geometry. The multiple choice questions test students on mathematical reasoning and proof.
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Activity
Maths Challenge

Maths challenge.net: Isosceles Trapezium

For Students 9th - 10th Standards
This is a "three star" geometry problem where prior knowledge of problem solving and thinking through proofs is recommended to solve this trapezoid inscribed in a semicircle problem.
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Activity
Maths Challenge

Maths challenge.net: Annulus

For Students 9th - 10th Standards
An annulus of a circle is defined and then a proof like problem is posed involving area and radius of circles.

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