Download Copies of Line Segments and Angles

Copies of Line Segments and
Angles
CK-12
Kaitlyn Spong
Say Thanks to the Authors
Click http://www.ck12.org/saythanks
(No sign in required)
To access a customizable version of this book, as well as other
interactive content, visit www.ck12.org
CK-12 Foundation is a non-profit organization with a mission to
reduce the cost of textbook materials for the K-12 market both
in the U.S. and worldwide. Using an open-content, web-based
collaborative model termed the FlexBook®, CK-12 intends to
pioneer the generation and distribution of high-quality educational
content that will serve both as core text as well as provide an
adaptive environment for learning, powered through the FlexBook
Platform®.
Copyright © 2014 CK-12 Foundation, www.ck12.org
The names “CK-12” and “CK12” and associated logos and the
terms “FlexBook®” and “FlexBook Platform®” (collectively
“CK-12 Marks”) are trademarks and service marks of CK-12
Foundation and are protected by federal, state, and international
laws.
Any form of reproduction of this book in any format or medium,
in whole or in sections must include the referral attribution link
http://www.ck12.org/saythanks (placed in a visible location) in
addition to the following terms.
Except as otherwise noted, all CK-12 Content (including CK-12
Curriculum Material) is made available to Users in accordance
with the Creative Commons Attribution-Non-Commercial 3.0
Unported (CC BY-NC 3.0) License (http://creativecommons.org/
licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated
herein by this reference.
Complete terms can be found at http://www.ck12.org/terms.
Printed: August 23, 2014
AUTHORS
CK-12
Kaitlyn Spong
www.ck12.org
C HAPTER
Chapter 1. Copies of Line Segments and Angles
1
Copies of Line Segments
and Angles
Here you will learn the difference between a construction and a drawing. You will also learn how to create copies of
line segments, angles, and triangles.
Use a straightedge to draw a triangle like the one below on your paper. Describe at least two ways to use a compass
and straightedge to copy the triangle.
Watch This
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/73745
https://www.youtube.com/watch?v=38dkb_0egjU Construct a Copy of an Angle
Guidance
As you have studied math, you have often created drawings. Drawings are a great way to help communicate a
visual idea. A construction is similar to a drawing in that it produces a visual outcome. However, while drawings
are often just rough sketches that help to convey an idea, constructions are step-by-step processes used to create
accurate geometric figures.
Constructions take us back over 2000 years to the ancient Greeks, before computers or other advanced technology.
Using only the tools of a compass and a straightedge, they discovered how to copy segments, angles and shapes,
how to create perfect regular polygons, and how to create perfect parallel and perpendicular lines. Today, learning
constructions is a way to apply your knowledge of geometric principles. You can do constructions by hand, or with
dynamic geometry software. In this concept, the focus is on hand constructions and making copies of segments,
angles, and triangles.
To create a construction by hand, there are a few tools that you can use:
1
www.ck12.org
1. Compass: A device that allows you to create a circle with a given radius. Not only can compasses help you
to create circles, but also they can help you to copy distances.
2. Straightedge: Anything that allows you to produce a straight line. A straightedge should not be able to
measure distances. An index card works well as a straightedge. You can also use a ruler as a straightedge, as
long as you only use it to draw straight lines and not to measure.
3. Paper: When a geometric figure is on a piece of paper, the paper itself can be folded in order to construct new
lines.
Example A
Use a straightedge to draw a line segment on your paper like the one shown below. Then, use your straightedge and
compass to copy the line segment exactly.
Solution: First use your straightedge and pencil to create a new ray.
Now, you have one endpoint of your line segment. Your job is to figure out where the other endpoint should go on
the ray. Use your compass to measure the width of the original line segment.
Now, move the compass so that the tip is on the endpoint of the ray.
2
www.ck12.org
Chapter 1. Copies of Line Segments and Angles
You can now see where the endpoint of the segment should lie on the ray. Draw a little arc with the compass to mark
where the endpoint should go.
You can use your straightedge to draw the copied line segment in a different color if you wish.
Note that in this construction, the compass was used to copy a distance. This is one of the primary uses of a compass
in constructions.
Example B
Use a straightedge to draw an angle on your paper like the one shown below. Then, use your straightedge and
compass to copy the angle exactly.
3
www.ck12.org
Solution: Keep in mind that what defines the angle is the opening between the two rays. The lengths of the rays are
not relevant.
Start by using your straightedge and pencil to draw a new ray. This will be the bottom of the two rays used to create
the angle.
Next, use your compass to make an arc through the original angle. It does not matter how wide you open your
compass for this.
Next, leave your compass open to the same width, and make a similar arc through the new ray.
4
www.ck12.org
Chapter 1. Copies of Line Segments and Angles
Now, you know that the second ray necessary to create the new angle will go somewhere through that arc. Measure
the width of the arc on the original angle using the compass.
Leave the compass open to the same width, and move it to the new angle.
Make a mark to show where the pencil on the compass intersects the arc.
5
www.ck12.org
Use a straightedge to draw another ray that passes through the point of intersection of the two compass markings.
You have now copied the angle exactly.
Example C
6
www.ck12.org
Chapter 1. Copies of Line Segments and Angles
An angle is created from two line segments. Use a straightedge to draw a similar figure on your paper. Then, use the
straightedge and compass to copy the figure exactly.
Solution: To copy this figure, you will need to copy both the line segments and the angle.
Start by copying the line segment on the bottom using the process outlined in Example A (draw a ray, use the
compass to measure the width of the line segment, mark off the endpoint on the ray).
Next, copy the angle using the process outlined in Example B (draw an arc through the angle and draw the same arc
through the new ray, measure the width of the arc, draw a new ray through the intersection of the two markings).
Finally, copy the second line segment by measuring its length using the compass and marking off the correct spot
for the endpoint.
7
www.ck12.org
You can now draw the copied segments in a different color for emphasis.
Concept Problem Revisited
To copy a triangle means to create a congruent triangle. There are four triangle congruence criteria that work for
any type of triangle: SSS, SAS, AAS, ASA. You can use SSS, SAS, or ASA combined with copying angles and line
segments to copy a triangle.
1. SSS: Copy one line segment. Copy the other two line segments so that their endpoints intersect. This
construction will be explored in Guided Practice #1.
2. SAS: Copy one line segment. Copy an angle from one of the endpoints of the line segment. Copy a second
line segment onto the ray created by the copied angle. Connect the endpoints to form the triangle. This is very
similar to Example C. This construction is explored in Guided Practice #2.
3. ASA: Copy one line segment. Copy two angles, one from each endpoint. The intersection of the angles will
produce the third vertex of the triangle. This construction is explored in Guided Practice #3.
Vocabulary
A drawing is a rough sketch used to convey an idea.
A construction is a step-by-step process used to create an accurate geometric figure.
A compass is a device that allows you to create a circle with a given radius. Compasses can also help you to copy
distances.
A straightedge is anything that allows you to produce a straight line. A straightedge should not be able to measure
distances. An index card works well as a straightedge. You can also use a ruler as a straightedge, as long as you only
use it to draw straight lines and not to measure.
8
www.ck12.org
Chapter 1. Copies of Line Segments and Angles
Guided Practice
You drew a triangle similar to the one below for the concept problem.
1. Copy your triangle using SSS.
2. Copy your triangle using SAS.
3. Copy your triangle using ASA.
Answers:
1. Start by copying one line segment. Here, the base line segment is copied.
Next, use the compass to measure the length of one of the other sides of the triangle.
9
www.ck12.org
Move the compass to the location of the new triangle and make an arc to mark the length of the second side of the
triangle from the correct endpoint.
Repeat with the third side of the triangle.
The point where the arcs intersect is the third vertex of the triangle. Connect to form the triangle.
10
www.ck12.org
Chapter 1. Copies of Line Segments and Angles
Note that with this method, you have only used the lengths of the sides of the triangle (as opposed to any angles) to
construct the new triangle.
2. Start by copying one line segment. Here, the base of the triangle is copied.
Next, copy the angle at one of the endpoints of the line segment.
Copy the second side of the triangle (that creates the angle you copied) onto the ray that you just drew.
11
www.ck12.org
Connect to form the triangle.
3. Start by copying one line segment.
Next, copy the angle at one of the endpoints.
12
www.ck12.org
Chapter 1. Copies of Line Segments and Angles
Copy the angle at the other endpoint of the line segment.
Connect to form the triangle.
Practice
1.
2.
3.
4.
5.
6.
What is the difference between a drawing and a construction?
What is the difference between a straightedge and a ruler?
Describe the steps for copying a line segment.
Describe the steps for copying an angle.
When copying an angle, do the lengths of the lines matter? Explain.
Explain the connections between copying a triangle and the triangle congruence criteria.
13
www.ck12.org
7.
8.
9.
10.
11.
12.
13.
14.
15.
Draw a line segment and copy it with a compass and straightedge.
Draw another line segment and copy it with a compass and straightedge.
Draw an angle and copy it with a compass and straightedge.
Draw another angle and copy it with a compass and straightedge.
Use your straightedge to draw a triangle. Copy the triangle using SSS ∼
=. Describe your steps.
Copy the triangle from #11 using SAS ∼
=. Describe your steps.
Copy the triangle from #11 using ASA ∼
=. Describe your steps.
Can you copy the triangle from #11 using AAS ∼
=? Explain.
Compare the methods for copying the triangle. Is one method easier than the others? Explain.
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
14
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. CC BY-NC-SA
. CC BY-NC-SA
. CC BY-NC-SA
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
. CC BY-NC-SA
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
. CC BY-NC-SA
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
. CC BY-NC-SA
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
CK-12 Foundation.
Author:
Author:
Author:
Author:
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
.
.
.
.
Author:
Author:
Author:
Author:
Author:
Author:
Author:
Author:
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
.
.
.
.
.
.
.
.
Author:
Author:
Author:
Author:
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
.
.
.
.
Author:
Author:
Author:
Author:
Author:
Author:
Author:
Author:
Author:
Author:
Author:
Author:
Author:
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
Kaitlyn Spong and Laura Guerin
.
.
.
.
.
.
.
.
.
.
.
.
.