Eligible Content M3.C.2.1.2


Help Me To:   plus

Identify/draw a line of symmetry in a two-dimensional figure

Did You Know?

A line of symmetry is an imaginary line that divides a figure in half.


Check What You Know First

Look at the figures and decide if the dashed line is a line of symmetry.  Write yes or no.

1)

 

 

2)

 

 

3)

 

 

4)

 

5)

 

 

6)

 

Key Vocabulary

A line of symmetry is an imaginary line that divides a figure into halves that match or divides the figure into two
congruent parts.

Congruent - Figures that have the same size and shape.

Rotational Symmetry - what a figure has when if it can be turned about a central point and still look the same in
at least two positions

 

Learn About It Now

A line of symmetry is an imaginary line that divides a figure into halves that match.  In other words, if you fold a figure along
a line of symmetry, both sides match.  Look at the following example.  You can fold the pentagon along its line of symmetry. 
Both halves will match.

In the problems that you did, numbers 2, 4 and 5 have a line of symmetry.  Look at the figures again. 

If you folded the figures along the dashed line, both sides would match. 

Problems 1, 3 and 6 do not have a line of symmetry. 

If you folded the figures along the dashed line, both sides would not match.

 

Here is another example of a figure that a line of symmetry.  In fact, this figure has two lines of symmetry.  When you fold
and unfold the figure, you can see that one side is a reflection of the other.  When a figure can be folded along a line so the two
parts are identical, the figure has line symmetry.

 

Some figures have one or more lines of symmetry.  Some figures have no lines of symmetry.  Look at
the examples below.

 

A figure can also have rotational symmetry if it can be turned about a central point and still look the same in at least two
different positions.  The figure below has rotational symmetry.

 

More Practice With Line of Symmetry 


Decide if the dashed line is a line of symmetry.  Write yes or no.

 

 

 

 

 

 

 

 

 

 

 

 

Websites to Check Out For Extra Practice

Click on this website to see and hear a lesson on symmetry.  This lesson is a good review of the concept of symmetry.
Once you have clicked on the site, scroll down and click on Teaching Model 15.9 symmetry.  Make sure you have turned
on your speakers.
http://www.eduplace.com/math/mw/models/tm_5.html

Click on this website to practice making a line of symmetry on a figure.
http://www.harcourtschool.com/activity/elab2004/gr4/19.html

Click on this website to see and hear a lesson on symmetry. This lesson provides excellent quizzes to test your knowledge of symmetry.
Make sure you have turned on your speakers.
http://www.linkslearning.org/Kids/1_Math/2_Illustrated_Lessons/4_Line_Symmetry/index.html

 

Other Fun Websites on Symmetry 


Click on this website to make a symmetrical butterfly
http://www.smm.org/sln/tf/s/symmetry/symmetry.html

Click on this website to draw a symmetrical picture.
http://www.geocities.com/ptmcg/Symmetry.html

Click on this website to learn about symmetry in two-dimensional shapes.  Scroll down to select Ask Hannah.
http://beaconlearningcenter.com/WebLessons/

Click on the following three sites from teachers network to view symmetry in the world around us.
http://www.teachersnetwork.org/dcs/math/symmetry/

Site on point symmetry
http://www.teachersnetwork.org/dcs/math/symmetry/Point/

Site on line symmetry
http://www.teachersnetwork.org/dcs/math/symmetry/Linesymmetry

Click on this website to learn a lot about symmetry through a slide show with fantastic pictures
There is a challenge game for you to play.
http://www.adrianbruce.com/Symmetry/