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Time Narration
00:00 Hello everybody. Welcome to this tutorial on Symmetrical Transformation in Geogebra.
00:06 In this tutorial we will learn Symmetrical transformations such as:
00:11 * Line symmetry
00:12 * Rotation symmetry
00:13 * and also learn to enlarge figure with scale and position.
00:17 We assume that you have the basic working knowledge of Geogebra.
00:21 If not, for relevant tutorials, please visit our website.
00:26 To record this tutorial, I am using Ubuntu Linux OS Version 11.10,
00:31 Geogebra Version
00:35 We will use the following Geogebra tools:
00:37 * Reflect Object about Line
00:39 * Rotate Object around Point by Angle
00:42 * Dilate object from a Point by Factor
00:45 * Semicircle through Two points
00:47 * Regular Polygon and
00:49 * Perpendicular bisector
00:51 Definition of Transformation-
00:53 Symmetrical transformation of a geometric figure is:
00:57 A change in its position, size or shape on a coordinate plane.
01:02 Original figure is called Object.
01:04 Transformed figure is called Image.
01:07 Reflection symmetry:
01:09 * Is also called as Line symmetry.
01:11 * A type of symmetry where one half is the reflection of the other half.
01:15 * You could fold the image and have both halves match exactly.
01:20 * Line of Symmetry is the line over which the figure is reflected.
01:24 Let's switch to Geogebra window.
01:27 Look on Dash home >> Media Apps >> under Type >> choose Education >> and Geogebra.
01:37 For this tutorial, I am closing the Algebric view.
01:40 Click on Close button on Algebric view.
01:47 Let's start with Line of symmetry.
01:50 First, let's construct an equilateral triangle.
01:53 Select Regular Polygon tool from the toolbar.
01:57 Click on drawing pad points A ,B, and enter 3 for the number of sides.
02:08 An equilateral triangle ABC is drawn.
02:11 Let's draw a perpendicular bisector to one of the sides of triangle.
02:15 Select Perpendicular Bisector Tool and click on side AC.
02:26 Select the Point tool and create a point inside the triangle.
02:31 Move the point D towards one of the vertices .
02:38 Right click on point D and select Trace On.
02:43 Select Reflect Object about Line tool from the tool bar.
02:48 Click on the point D.
02:49 This will highlight point D.
02:52 Click on Perpendicular Bisector.
02:55 This will produce reflected image D' on the other side of perpendicular bisector.
03:01 D' is mirror image of point D.
03:04 Set Trace On for the point D.
03:08 Let us move the point D along the triangle, using Move tool.
03:11 Click on the first option under Move tool from the toolbar.
03:22 Click on figure with the mouse.
03:25 Drag it tracing the triangle .
03:28 Now release the mouse button.
03:31 What do you notice ?
03:32 Here perpendicular bisector is the line of symmetry.
03:36 D is the object and D' is the image.
03:39 Let's reflect a semicircle about a line.
03:43 Let's draw a semicircle.
03:44 Click on the Semicircle through Two points tool. Mark point E and then F.
03:56 Click on segment between two points.
04:02 Mark points G and H. A line is drawn.
04:06 Let's change the property of the line.
04:08 Right click on the line, Object Properties. Click on Style, change Style.
04:21 Select Reflect Object about Line tool from the toolbar.
04:27 Click on the semicircle EF.
04:31 Click on line GH.
04:34 This will produce the reflected image E'F' on the other side of line GH. What does the figure look like now ? It looks like a circle.
04:45 Let us save this file now.
04:47 Click on File >> Save As.
04:50 I will type the file name as Line-symmetry and click on Save.
05:05 Next, let us learn to Rotate the Object around a Point by Angle.
05:12 Definition of Rotation-
05:15 A rotation is a transformation that turns a figure around a fixed center by an angle.
05:21 If the figure appears unchanged then the figure has rotation symmetry.
05:29 You can rotate object at any degree measure. Rotation can be clockwise and counterclockwise.
05:39 Let's open a new Geogebra window.
05:41 click on File >> New.
05:47 Let us construct a square.
05:49 click on Regular Polygon tool from the toolbar.
05:55 Click on the drawing pad.
05:57 Mark points A and B.
05:59 A dialog box opens.
06:01 Click on OK.
06:03 A square ABCD is drawn.
06:05 Click on Rotate Object around a Point by Angle tool.
06:13 Click on the Square ABCD.
06:16 This will highlight the square.
06:18 Next Click on any one of the vertices.
06:20 I will click on A.
06:23 A dialog box opens.
06:25 Type 60 in the Angle field
06:30 Select °(Degree) from first drop down list.
06:35 Select the option clockwise. Click on OK.
06:40 This will rotate the square clockwise at the point of selection, with the angle of 60°.
06:44 The rotated image A`B`C`D` is formed.
06:49 Let's move this figure aside using Move tool.
07:00 Next, let's dilate or enlarge object from point by factor.
07:09 Dilation:
07:11 Dilation or enlargement is a transformation
07:14 in which a figure is enlarged using a scale factor.
07:23 Let's draw a triangle using the Polygontool,
07:28 E , F , G. Click on E again to complete the triangle.
07:36 Click on New Point tool and
07:40 mark a point H.
07:44 Click on Dilate Object from Point by Factor tool.
07:51 Click on the triangle EFG.
07:54 This will highlight the triangle.
07:55 Click on the point 'H'.
07:57 A dialog box opens.
08:00 Type value of 2 in the number field.
08:04 Click on OK.
08:09 This will dilate or enlarge the object twice.
08:16 Click on segment between two Points, join points H,E,E'.
08:33 join points H,G,G'.
09:01 join points H,F,F'.
09:15 Here, you can see that H is the point of dilation.
09:21 You can enlarge object as many number of times as you wish, by typing the value of Factor.
09:28 Let us save this file now.
09:30 Click on File >> Save As.
09:33 I will type the file name as Dilate-triangle.
09:48 Click on Save. With this we come to the end of this tutorial.
09:55 Let's summarize.
09:58 In this tutorial we learnt:
10:00 * Reflection about a line.
10:02 * Rotation of an object at a point.
10:05 * Enlargement of an object by a scale factor.
10:09 As an assignment I would like you to:
10:11 Draw a pentagon.
10:12 Use Regular Polygon tool to draw. (Hint:sides=5).
10:17 Draw a perpendicular bisector to one of the sides of the pentagon.
10:21 Create a point inside the pentagon.
10:25 Set Trace On for the point.
10:27 Get reflection of the point about the perpendicular bisector.
10:31 Set Trace On for the image point.
10:34 Trace the pentagon to see if you have selected the correct line of symmetry.
10:44 Rotate the original pentagon counter clockwise in 135° at a point.
10:49 Dilate the pentagon at a point by the factor of 3.
10:56 The assignment should look like this.
11:03 Watch the video available at this URL.
11:06 It summarizes the Spoken Tutorial project.
11:09 If you do not have good bandwidth,you can download and watch it.
11:12 The Spoken Tutorial Project Team : Conducts workshops using the spoken tutorials.
11:17 Gives certificates to those who pass an online test.
11:20 For more details, please write to
11:26 Spoken Tutorial Project is a part of the Talk to a Teacher project.
11:29 It is supported by the National Mission on Education through ICT, MHRD, Government of India.
11:35 More information on this Mission is available at this link.
11:39 This is Neeta Sawant from SNDT University Mumbai, signing off.

Thanks for joining.

Contributors and Content Editors

Madhurig, Minal, Mousumi, PoojaMoolya, Pratik kamble, Sandhya.np14