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Activity
Maths Challenge

Maths challenge.net: Equal Angles

For Students 9th - 10th Standards
A geometric proof. Prove two angles in this model are equal in measure.
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Website
National Council of Teachers of Mathematics

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

For Students 9th - 10th Standards
A response to an inquiry of how to prove a two column geometric proof problem at the Math Forum. This site gives a description of what a makes a proof and an example of a two column proof.
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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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Lesson Plan
Science Education Resource Center at Carleton College

Serc: Pythagorean Theorem Investigations

For Teachers 9th - 10th Standards
In this activity, students will gain an understanding of the Pythagorean theorem and will recognize the variety of ways in which theorems can be proved algebraically, geometrically and visually.
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Handout
University of British Columbia

University of British Columbia: Proof of the Pythagorean Theorem

For Students 9th - 10th Standards
A geometric model that proves the Pythagorean Theorem in a step-by-step diagram that students can advance at their own pace. Requires Java.
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Activity
Maths Challenge

Maths challenge.net: Odd Vertices

For Students 9th - 10th Standards
A "three star geometry problem" requiring knowledge of how to complete geometric proofs. The problem explains what the order of a vertex is and asks for the proof of a generalization.
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Activity
Maths Challenge

Maths challenge.net: Platonic Solids

For Students 9th - 10th Standards
A "three star geometry problem" requiring knowledge of how to complete geometric proofs to prove that there are no more than five regular convex polyhedra.
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Activity
Maths Challenge

Maths challenge.net: Quadrilateral Parallelogram

For Students 9th - 10th Standards
A "three star geometry problem" requiring knowledge of how to complete geometric proofs and some prior math knowledge. This problem asks to prove that the mid points of any quadrilateral form a parallelogram.
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Activity
Maths Challenge

Maths challenge.net: Parallelogram Property

For Students 9th - 10th Standards
A "three star geometry problem" requiring knowledge of how to complete geometric proofs properties of parallelogram.
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Interactive
Shodor Education Foundation

Shodor Interactivate: Squaring the Triangle

For Students 9th - 10th Standards
Learn about how the Pythagorean Theorem works through investigating the standard geometric proof.
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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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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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Activity
Maths Challenge

Maths challenge.net: Right Triangle Equal Parts

For Students 9th - 10th Standards
A geometry proof problem involving a right triangle and finding angles of equal measure.
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Activity
Maths Challenge

Maths challenge.net: Inscribed Rectangle

For Students 9th - 10th Standards
This is a proof problem, considered a "three star" geometry problem requiring knowledge of proofs and properties of circles to solve this equal area of inscribed polygons problem.
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Handout
Maths Challenge

Maths challenge.net: Three Circles

For Students 9th - 10th Standards
This is a proof problem, considered a "three star" geometry problem requiring knowledge of proofs and properties of circles.
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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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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: Tri Angles

For Students 9th - 10th Standards
A geometry proof involving exterior angles of a triangle.
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Activity
Maths Challenge

Maths challenge.net: Rectangular Circles

For Students 9th - 10th Standards
An area problem involving finding the area of a rectangle and a circle. The problem may be made into a general proof as well.
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Activity
Maths Challenge

Maths challenge.net: Perpendicular Construction

For Students 9th - 10th Standards
This is a "three star" geometry problem where prior math problem skills and proof experience is recommended to solve this "Perpendicular Construction" problem.
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Activity
Maths Challenge

Maths challenge.net: Alley Ladders

For Students 9th - 10th Standards
This is a "three star" geometry problem where prior math problem skills and proof experience is recommended to solve this relationship between the inverses of heights.
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Activity
Maths Challenge

Maths challenge.net: Triangle in a Square

For Students 9th - 10th Standards
A "three star" geometry problem requiring some prior knowledge in math and proofs to maximize the area of an inscribed triangle in terms of the hypotenuse.
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Activity
Maths Challenge

Maths challenge.net: Maximum Square

For Students 9th - 10th Standards
A challenging proof like geometry of finding the square inscribed in a triangle.
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Activity
Maths Challenge

Maths challenge.net: Bag of Balls

For Students 9th - 10th Standards
A "three star" geometry problem which requires prior math problem solving skills and proof writing skills to solve this "Bag of Balls" radius of balls problem.

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