Circles

Lesson 7

Math

Unit 7

10th Grade

Lesson 7 of 14

Objective


Prove properties of angles in a quadrilateral inscribed in a circle.

Common Core Standards


Core Standards

  • G.C.A.3 — Construct the inscribed and circumscribed circles of a triangle, and prove properties of angles for a quadrilateral inscribed in a circle.

Foundational Standards

  • G.CO.D.13

Criteria for Success


  1. Use intercepted arcs to show that opposite angles of an inscribed quadrilateral are supplementary. See Unit 7 Glossary for a visual.
  2. Use auxiliary radii to show that opposite angles of an inscribed quadrilateral are supplementary. See Unit 7 Glossary for a visual.
  3. Determine whether a given quadrilateral can be inscribed in a circle.
  4. Find missing angle measures for a quadrilateral inscribed in a circle. 

Tips for Teachers


  • The following resources may be helpful in your planning since it describes more complete classifications of quadrilaterals than typical: Cut the Knot, Alexander Bogomolny, “Classification of Quadrilaterals."
  • This lesson connects to Unit 1, Lesson 15, which inscribes triangles in circles, by taking that lesson one step further by inscribing quadrilaterals in circles. For an extension, you could inscribe triangles, squares, and regular hexagons in circles. 
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Anchor Problems

25-30 minutes


Problem 1

Below is a quadrilateral inscribed in a circle, also known as a cyclic quadrilateral.

Describe the relationship between the opposite angles $$\angle CDB$$ and $$\angle CEB$$  in the cyclic quadrilateral using the intercepted arcs. 

Guiding Questions

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References

GeoGebra Geo_U7_L7_AP1

Geo_U7_L7_AP1 by Kerry Taylor is made available by GeoGebra under the CC BY-NC-SA 3.0 license. Copyright © International GeoGebra Institute, 2013. Accessed Sept. 19, 2018, 1:45 p.m..

Problem 2

Below is the same cyclic quadrilateral as shown in Anchor Problem #1. Show, using the radii marked and the angle measures marked, the relationship between opposite angles.

Guiding Questions

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References

GeoGebra Geometry - 8.7 AP2

Geometry - 8.7 AP2 by Match Fishtank is made available by GeoGebra under the CC BY-NC-SA 3.0 license. Copyright © International GeoGebra Institute, 2013. Accessed June 13, 2017, 11:22 a.m..

Target Task

5-10 minutes


What value of $$x$$ guarantees that the quadrilateral shown in the diagram below is cyclic? Explain your reasoning.

References

EngageNY Mathematics Geometry > Module 5 > Topic E > Lesson 20Exit Ticket, Question #1

Geometry > Module 5 > Topic E > Lesson 20 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..

Modified by Fishtank Learning, Inc.

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.

  • Include a problem where the students are required to use arcs to describe the interior angles of a cyclic triangle.

Next

Define and determine properties of tangents and secants of circles to solve problems with inscribed and circumscribed triangles.

Lesson 8
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Lesson Map

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

Topic A: Equations of Circles

Topic B: Angle and Segment Relationships in Inscribed and Circumscribed Figures

Topic C: Arc Length, Radians, and Sector Area

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