Going Halvesies

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SWBAT use straight-edge and compass to construct a (segment) bisector and verify its properties. Students will understand how geometric objects may be defined in terms of other objects and identified using geometric notation.

Big Idea

What are the properties of a bisector? Students see for themselves--and find that a compass is an efficient instrument for comparing distances.

Lesson Opener

5 minutes

Team Warm-up

The Warm-Up prompt for the lesson asks students to recall the properties of bisectors.

This lesson opener follows our Team Warm-up routine, with students writing individual answers in their Learning Journals.  I display the prompt using the Slideshow for the lesson.


Displaying the lesson Agenda and Learning Targets, I tell the class that today we will learn how to construct a bisector and to use constructions to investigate their properties.

Constucting a Bisector

10 minutes

As in the previous lesson, I use Guided Notes to demonstrate the construction of a bisector.  Students complete the illustrations in their notes as they follow along.

I demonstrate the Construction of a Bisector in this video.


Practice & Investigation

20 minutes

I display the instructions and distribute the activity.  The goal is for students to practice the construction of a bisector and to use constructions to verify their properties.

This activity uses the Rally Coach format. 

Summarizing - Defining Geometric Objects

15 minutes

I ask students to get out their Guided Notes: Constructions/ Defining Geometric Objects.  Now that we know what lines and circles are, we can define other objects--segments, rays, and arcs--with precision (MP6).  We complete the final page of the notes: Defining Geometric Objects.

Displaying the guided notes with the help of an interactive whiteboard, I lead the class in completing the definitions and the examples.  I encourage students to use straight-edge and compass to construct the diagrams, although this is not strictly necessary.



Lesson Close and Homework

4 minutes

Team Size-Up

The lesson close follows our Team Size-Up routine.  The prompt asks students to explain what constructions are and why we learn them.  This essential question for the unit was answered in the notes.


Homework Set 2 problem #23 asks students to practice some of the constructions they have just learned.  Problem #24 reviews algebra concepts (slope).  In addition, I assign Portfolio Problem 2- Placing a Call, which students should now be able to answer completely.