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Handout
Lockport City School District

Reasons for Geometric Statement/Reason Proofs

For Students 8th - 11th Standards
Stuck trying to remember the formal language of a geometric proof? Never fear, this handout has them all ready to go. The reasons are sectioned by topic so this handy guide is ready when you are to tackle those two column proofs. 
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Lesson Plan
EngageNY

Triangle Congruency Proofs (part 2)

For Teachers 9th - 10th Standards
Looking to challenge your students that have mastered basic triangle congruence proofs? A collection of proofs employ previously learned definitions, theorems, and properties. Pupils draw on their past experiences with proofs to...
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Instructional Video0:53
Corbett Maths

Angles in the Same Segment – Proof

For Students 8th - 12th Standards
If angles intercept the same arc, the angles must be the same size. The quick video talks through the proof of showing the reason two inscribed angles that intersect the same arc have the same measurement. Pupils then create their own...
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Activity
Education Development Center

Proof with Parallelogram Vertices

For Teachers 8th - 10th Standards
Geometric figures are perfect to use for proofs. Scholars prove conjectures about whether given points lie on a triangle and about midpoints. They use a provided dialogue among fictional learners to frame their responses.
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Lesson Plan
EngageNY

Triangle Congruency Proofs (part 1)

For Teachers 9th - 10th Standards
Can they put it all together? Ninth graders apply what they know about proofs and triangle congruence to complete these proofs. These proofs go beyond the basic triangle congruence proofs and use various properties, theorems, and...
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Interactive
CK-12 Foundation

Proofs: Angle Pairs and Segments—The Three Angle Problem

For Students 9th - 11th
Finding the sum of the measures of three angles is easy, unless you have no clue what the measures are. Learners use an interactive diagram to see a geometric problem in a different way. A set of challenge questions takes them through...
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Unit Plan
Mathematics Vision Project

Geometric Figures

For Teachers 10th - 12th Standards
Logical thinking is at the forefront of this jam-packed lesson, with young mathematicians not only investigating geometric concepts but also how they "know what they know". Through each activity and worksheet, learners wrestle with...
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Instructional Video16:33
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2
Flipped Math

More with Proofs

For Students 9th - 12th Standards
Proofs may be as easy as 1, 2, 3 ... maybe. Pupils participate in creating four example proofs. The presentation uses a list of geometric properties to develop the proofs by filling in both the statements and reasons. Scholars practice...
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Worksheet
Academic Magnet High School

Parallel Lines Proofs Practice

For Students 8th - 11th Standards
Here is a worksheet that lines up perfectly with the skills needed to finish a geometric proof. Eleven problems are given to see if learners can prove that lines are parallel or angles are congruent. 
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Lesson Plan
EngageNY

Informal Proofs of Properties of Dilations

For Teachers 8th Standards
Challenge the class to prove that the dilation properties always hold. The lesson develops an informal proof of the properties of dilations through a discussion. Two of the proofs are verified with each class member performing the...
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Lesson Plan
EngageNY

Informal Proof of the Pythagorean Theorem

For Students 8th Standards
Prove the Pythagorean Theorem using multiple informal proofs. Scholars first develop an understanding of the origins of the Pythagorean Theorem through proofs. They round out the instructional activity by using the theorem to find...
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Lesson Plan
EngageNY

Solve for Unknown Angles—Angles and Lines at a Point

For Teachers 9th - 10th Standards
How do you solve for an unknown angle? In this sixth installment of a 36-part series, young mathematicians use concepts learned in middle school geometry to set up and solve linear equations to find angle measures.
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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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Worksheet
Curated OER

Proofs

For Students 8th - 11th
In this geometric proof instructional activity, 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...
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Worksheet
Geometry Accelerated

Accelerated Geometry Review Sheet

For Students 8th - 10th Standards
Your geometry learners use their knowledge of various geometric concepts to write proofs. Starting with givens containing parallel line segments with transversals and triangles and quadrilaterals, and the mid-point and distance formulas;...
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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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Unit Plan
Mathematics Vision Project

Module 2: Congruence, Construction and Proof

For Teachers 9th - 12th Standards
Construct yourself a winning geometry unit. A set of lessons introduces geometry scholars to constructions and proofs with compasses and straightedges. It also covers triangle congruence through transformations. This is the second of...
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Lesson Plan
EngageNY

Informal Proof of AA Criterion for Similarity

For Teachers 8th Standards
What does it take to show two triangles are similar? The 11th segment in a series of 16 introduces the AA Criterion for Similarity. A discussion provides an informal proof of the theorem. Exercises and problems require scholars to apply...
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Lesson Plan
EngageNY

Angle Sum of a Triangle

For Students 8th Standards
Prove the Angle Sum Theorem of a triangle using parallel line and transversal angle relationships. Pupils create a triangle from parallel lines and transversals. They find angle measures to show that the angles of a triangle must total...
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Unit Plan
Mathematics Vision Project

Module 3: Geometric Figures

For Teachers 9th - 12th Standards
It's just not enough to know that something is true. Part of a MVP Geometry unit teaches young mathematicians how to write flow proofs and two-column proofs for conjectures involving lines, angles, and triangles.
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Lesson Plan
EngageNY

Unknown Angle Proofs—Proofs with Constructions

For Teachers 9th - 10th Standards
Provide your emerging mathematicians with the tools to learn as they incorporate auxiliary lines to solve unknown angle proofs in this continuing segment. They decipher information from a diagram to uncover the missing pieces and...
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Worksheet
Curated OER

Geometric Proofs

For Students 10th - 11th
In this geometric proofs worksheet, students prove supplementary, complimentary, and congruent angles from given models and information. This four-page worksheet contains six multi-step problems.
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Worksheet
Curated OER

Geometric Proofs

For Students 10th - 11th
In this geometric proof worksheet, students use geometric theorems and rules to prove given statements. They prove that given lines and angles are similar. This five-page worksheet contains ten problems.
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Assessment
Inside Mathematics

Quadrilaterals

For Teachers 9th - 12th Standards
What figure is formed by connecting the midpoints of the sides of a quadrilateral? The geometry assessment task has class members work through the process of determining the figure inscribed in a quadrilateral. Pupils use geometric...