Congruence in Two Dimensions

Lesson 16

Math

Unit 2

10th Grade

Lesson 16 of 18

Objective


Use criteria for triangle congruence to prove relationships among angles and sides in geometric problems.

Common Core Standards


Core Standards

  • G.CO.C.9 — Prove theorems about lines and angles. Theorems include: vertical angles are congruent; when a transversal crosses parallel lines, alternate interior angles are congruent and corresponding angles are congruent; points on a perpendicular bisector of a line segment are exactly those equidistant from the segment's endpoints.
  • G.SRT.B.5 — Use congruence and similarity criteria for triangles to solve problems and to prove relationships in geometric figures.

Foundational Standards

  • 8.G.A.2

Criteria for Success


  1. Annotate a diagram with all congruent relationships using appropriate notation. 
  2. Develop a series of statements and evidence that prove that two triangles are congruent by triangle congruence criteria established. 
  3. Identify and develop proofs when congruence criteria is met in diagrams where triangles are embedded. 
  4. Identify missing measures directly and algebraically in triangles where congruence criteria is met.
  5. Identify errors in proof where the congruence criteria is not met, but used in arguments. Correct reasoning. 
  6. Use auxiliary lines to create congruent relationships and establish relationships within geometric diagrams.
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Anchor Problems

25-30 minutes


Problem 1

Triangle A has a side that is one inch long, and has angles with measures of $${90^{\circ}}$$ and $${20^{\circ}}$$.  

If Triangle B is drawn with the same properties as Triangle A, will it be congruent to Triangle A? Explain your reasoning.

Guiding Questions

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References

MARS Formative Assessment Lessons for High School Evaluating Conditions for Congruency

Evaluating Conditions for Congruency from the Classroom Challenges by the MARS Shell Center team at the University of Nottingham is made available by the Mathematics Assessment Project under the CC BY-NC-ND 3.0 license. Copyright © 2007-2015 Mathematics Assessment Resource Service, University of Nottingham. Accessed Aug. 10, 2017, 4:08 p.m..

Modified by Fishtank Learning, Inc.

Problem 2

Given: $${AB=AC}$$$${RB=RC}$$

Prove: $${SB=SC}$$

Guiding Questions

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References

EngageNY Mathematics Geometry > Module 1 > Topic D > Lesson 27Exercise 1

Geometry > Module 1 > Topic D > Lesson 27 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Target Task

5-10 minutes


Given: $$M$$ is the midpoint of $${\overline {GR}}$$, $${\angle G \cong \angle R}$$

Prove: $$\triangle GHM \cong \triangle RPM$$

References

EngageNY Mathematics Geometry > Module 1 > Topic D > Lesson 27Exit Ticket

Geometry > Module 1 > Topic D > Lesson 27 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Additional Practice


The following resources include problems and activities aligned to the objective of the lesson that can be used for additional practice or to create your own problem set.

Next

Prove that the opposite sides and opposite angles of a parallelogram are congruent.

Lesson 17
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Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

Topic A: Introduction to Polygons

Topic B: Rigid Motion Congruence of Two-Dimensional Figures

Topic C: Triangle Congruence

Topic D: Parallelogram Properties from Triangle Congruence

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