Susan Chaffee
Geometry Chapter 1
Spring 2009
Lesson 4 – Introduction and sections 1.7
This lesson introduces the student to geometry and the foundations.
Unit: Chapter 1 Tools of Geometry
Lesson: Section 1.7 Basic Constructions
Lesson Goals: Learn to use compass and straightedge for construction of angles and segments
Lesson Objectives:
 Given a compass and straightedge TLWBAT construct a segment congruent to another.
Enduring Understanding:
Essential Questions:
 Why is a compass and straightedge superior to using only a ruler or a protractor for creating
congruent angles and segments.
Materials and/or Special Notes:
 Smart Board lesson notes, Textbook, ruler
Prior Knowledge:
 Students know
Write on the board 1.7 Basic Constructions
(Definition) Construction – using a straightedge and compass to draw a geometric figure.
Motivation:
The compass is able to give an exact measurement, superior to using a msmt. tool such as ruler or
protractor with markings on them. (Demonstrate). The Greek mathematicians used this form of
construction for accuracy. Different than a drawing, architects use these tools for construction.
Straight edge has no markings, only for drawing straight line.
Compass is used for drawing arcs and measuring lines.
Today’s objective, use compass and straightedge to:
1.
2.
3.
4.
construct congruent segments
construct congruent angles
bisect segments
bisect angles
Procedures (lesson outline):
INTO (Warm-up/Review/Connections: (5 minutes)
Draw several points and practice drawing various size arcs.
Susan Chaffee
Geometry Chapter 1
Spring 2009
Might also want to refresh notation for congruent.
TEACHER and STUDENT ACTIVITIES :
1. Construct congruent segments
Given a segment, ̅̅̅̅
𝐴𝐵 construct ̅̅̅̅
𝐶𝐷 so that ̅̅̅̅
𝐴𝐵 ≅ ̅̅̅̅
𝐶𝐷
Step 1. Draw a point C, if it is not given.
Step 2. Draw a ray CD.
Step 3. Open compass from A to B
Step 4. With same setting, put compass point on C and draw arc over ray, this is point D.
Group activity. Draw a segment AB, any length you’d like. Trade with partner and draw a new segment
congruent to AB on the paper.
2. Construct congruent angles
Given an angle ∠𝐴, construct a second angle congruent to the first.
Step 1. Draw a ray with endpoint S.
Step 2. Place compass endpoint on A and draw an arc that intersects with both sides of A. Label
these points B and C
Step 3. Without changing compass setting, place point on S and draw an arc that intersects the
ray, label the point of intersection as R
Step 4. Now change compass setting, place point on B and adjust compass to measure length BC
Step 5. Without changing setting, place point on R and make arc that intersects arc from step 3.
Label as T
Step 6. Draw ray from S through the point T in step 5.
Lesson Closure:
Learning Log: Write steps in your own words for bisecting an angle and bisecting a segment. Use
drawings to show the arcs in each step.
Assignments:
Assessment:
 Formative: Learning Log.
 Summative:
Lesson Accommodations: