Lesson 9
Speedy Delivery
Lesson Narrative
In this lesson, students build on their experiences with perpendicular bisectors to answer questions about allocating resources in a realworld situation (MP4). To complete more steps in the mathematical modeling cycle, use the optional activity Now Who Is Closest? Then students study a tessellation (an arrangement of figures that cover the entire plane), create a Voronoi diagram by applying perpendicular bisectors, and conjecture that the Voronoi diagram of a tessellation is also a tessellation.
Some of the activities in this lesson work best when each student has access to GeoGebra Geometry from Math Tools, because students are using perpendicular bisectors to determine which regions of a map are closest to certain points. In Who Is Closest?, they do this with 3 and 4 points, but doing it with more in Now Who is Closest? will require help from technology.
Learning Goals
Teacher Facing
 Choose geometric methods to solve design problems.
 Construct perpendicular bisectors and explain (in writing) how they are used to solve problems.
Student Facing
 Let’s use perpendicular bisectors.
Required Materials
Required Preparation
Acquire computers or tablets that can run GeoGebra Geometry from Math Tools, with one for every 2–3 students. The digital version is recommended for all classes over the paper and pencil version.
Ensure that students have at least 4 colors in their toolkits if they will be doing the paper and pencil version of Who is Closest?.
Learning Targets
Student Facing
 I can construct perpendicular bisectors to help solve problems.
 I can use my geometry knowledge to solve problems.
CCSS Standards
Building On
Addressing
Building Towards
Glossary Entries

tessellation
An arrangement of figures that covers the entire plane without gaps or overlaps.
Print Formatted Materials
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Student Task Statements  docx  
Cumulative Practice Problem Set  docx  
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Teacher Presentation Materials  docx  
Blackline Masters  zip 