View source for Geogebra/C3/Relationship-between-Geometric-Figures/English-timed

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|'''Time'''
|'''Narration'''

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||00:00
||Hello. 

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||00:01
||And welcome to the spoken tutorial on '''Relationship between different Geometric Figures in Geogebra'''.

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||00:07
||We assume that you have the basic working knowledge of '''Geogebra'''.  

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||00:11
||If not, please go through the '''Introduction to Geogebra''' tutorial before proceeding further.

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||00:18
||Please note that the intention to teach this tutorial is not to replace the actual compass box. 

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||00:24
||Construction in '''Geogebra''' is done with the view to understand the properties.

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||00:29
||In this tutorial, we will learn  to construct
 
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||00:32
||'''cyclic quadrilateral''' and '''incircle'''.

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||00:35
||To record this tutorial, I am using '''Linux operating system'''  

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||00:39
||'''Ubuntu Version  10.04 LTS''' 

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||00:43
||and '''Geogebra Version 3.2.40.0.''' 

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||00:48
||We will use the following Geogebra tools for  the construction:
* '''Compass'''

* '''Segment between Two Points'''

* '''Circle with Center through Point'''

* '''Polygon'''

* '''Perpendicular Bisector'''

* '''Angle Bisector''' and

* '''Angle'''.

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||01:02
||Let us switch on to the '''Geogebra''' window.

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||01:05
||To do this, let us click on '''Applications''', '''Education''' and '''Geogebra'''. 

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||01:13
||Let me resize this window.

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||01:18
||Click on the '''Options''' menu, click on '''Font Size''' and then on '''18''' point to make the figure clear.

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||01:25
||Let us construct a cyclic quadrilateral.

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||01:27
|| To do this, let us select the '''Regular Polygon''' tool from the tool bar, click on the '''Regular Polygon''' tool, click on any two points on the drawing pad.

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||01:38
||We see that a dialog box opens with a default value '''4'''.

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||01:42
||Click '''OK'''. 

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||01:43
||A square  '''ABCD''' is drawn. 

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||01:46
||Let's tilt the square using the '''Move''' tool which is at the left corner.

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||01:51
||Select the '''Move''' tool from the tool bar, click on the '''Move''' tool.

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||01:56
||Place the mouse pointer on  '''A''' or on '''B'''. I will choose '''B'''. 

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||02:01
||Place the mouse pointer on '''B''' and drag it with the mouse. We see that the square is in the tilted position now.

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||02:10
||Let's construct a perpendicular bisector to the segment '''AB'''. 

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||02:15
||To do this, let's select  '''Perpendicular Bisector'''  tool from the tool bar.

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||02:20
||Click on the '''Perpendicular Bisector''' tool. 

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||02:22
||Click on the point '''A''' 

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||02:24
||and then on  point'''B'''. 

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||We see that a perpendicular bisector is drawn.

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||02:30
||Let's construct a second perpendicular bisector to segment '''BC'''. To do this,  

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||02:36
||select  '''Perpendicular Bisector'''  tool from the tool bar, click on the  '''Perpendicular Bisector'''  tool.

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||Click on the point '''B''' 

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||02:44
||and then  on point '''C'''. 

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||02:46
||We see that the perpendicular bisectors intersect at a point.

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||02:50
||Let us mark this point as '''E'''.

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||02:54
||Let's now construct a circle with centre as '''E''' and which passes through '''C'''.

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||03:01
||Let's select the '''Circle with Centre through Point''' tool from tool bar, click on the '''Circle with Centre through Point''' tool.

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||03:09
||Click on point '''E''' as centre and which passes through '''C'''. Click on the point '''E''' and then on point '''C'''.

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||03:18
||We see that the circle will pass through all the vertices of the quadrilateral. A cyclic quadrilateral is drawn.

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||03:29
||Do you know that the cyclic quadrilateral has maximum area among all the quadrilaterals of the same sequence of side lengths?

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||03:37
||Let's use the '''Move''' tool, to animate the figure.

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||03:42
||To do this, let's select the '''Move''' tool from the tool bar, click on the '''Move''' tool. Place the mouse pointer on '''A''' or '''B'''. I will choose '''A'''.
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||03:52
||Place the mouse pointer on '''A''' and drag it with the mouse to animate,

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||03:58
||to verify that the construction is correct.

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||04:01
||Let's now save the file.  

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||04:04
||Click on '''File''' >> '''Save As'''.  

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||04:07
||I will type the file name as '''cyclic_quadrilateral'''. 

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||04:21
||and click on '''Save'''.

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||04:23
||Let us now open a new '''geogebra''' window to construct an incircle. 

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||04:28
||To do this let's select on '''File''' and '''New'''.

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||04:35
||Let's now construct a triangle. To do this, let's select the '''Polygon''' tool from the tool bar, click on the '''Polygon''' tool.
 
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||Click on the points '''A,B,C''' and '''A''' once again, to complete the triangle figure.  

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||04:52
||Let's measure the angles for this triangle.  

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||04:55
||To do this, let's select the '''Angle''' tool from the tool bar, click on the '''Angle''' tool.

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||05:00
||Click on the points '''B, A, C''' , '''C, B, A''' and '''A, C, B'''.

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||05:15
||We see that the angles are measured.

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||05:18
||Lets now construct angle bisectors to these angles. 

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||05:21
||Select the '''Angle Bisector''' tool from the tool bar, 

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||05:25
||click on the '''Angle Bisector''' tool. Click on the points '''B, A, C'''.

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||05:32
||Let's select the '''Angle Bisector''' tool again from the tool bar to construct second angle bisector.

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||05:39
||Click on the '''Angle Bisector''' tool from the tool bar, click on the points A, B, C.

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||05:48
||We see that the two angle bisectors intersect at a point .

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||05:52
||Let's mark this point as '''D'''.

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||05:55
||Let's now construct a perpendicular line which passes through point '''D''' and segment '''AB'''.

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||06:02
||Select '''Perpendicular Line''' tool from tool bar, click on the '''Perpendicular Line''' tool, click on the point '''D''' and then on segment '''AB'''.

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||06:12
||We see that the perpendicular line intersects segment '''AB''' at a point.

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||06:17
||Let's mark this point as '''E'''.

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||06:20
||Let's now construct a circle with centre as '''D''' and which passes through '''E'''.

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||06:27
||Let's select the '''Compass''' tool from tool bar , click on the '''Compass''' tool, click on the point D as centre and DE as radius.

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||06:37
||Click on the point '''D''' and then on point '''E''' and '''D''' once again to complete the figure.

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||06:46
||We see that the circle touches all the sides of the triangle.

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||06:50
||An incircle is drawn.

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||06:53
||With this, we come to an end of this tutorial.
  
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||06:57
||To Summarize: 

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||07:02
||in this tutorial, we have learnt to construct 

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||cyclic quadrilateral and

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||incircle using the Geogebra tools.

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||07:10
||As an assignment, I would like you to draw a triangle ABC.

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||07:15
||Mark a point '''D''' on '''BC''', join '''AD'''. 

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||07:19
||Draw incircles  from triangles '''ABC''', '''ABD''' and '''CBD''' of radii r, r1 and r2 . 

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||07:28
||BE is the height 'h'. 

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||Move the vertices of the triangle '''ABC''',

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||07:33
||to verify the relation: 

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||(1 -2r1/h)*(1 - 2r2/h) = (1 -2r/h) 

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||07:43
||The output of the assignment should look like this. 

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||07:52
||Watch the video available at this URL.

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||07:55
||It summarizes the Spoken Tutorial project.

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||07:57
||If you do not have good bandwidth, you can download and watch it. 

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||08:02
||The Spoken Tutorial Project Team :Conducts workshops using spoken tutorials.

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||08:06
||Gives certificates to those who pass an online test. 

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||08:09
||For more details, contact us contact@spoken-tutorial.org. 

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||08:16
||Spoken Tutorial Project is a part of Talk to a Teacher project. 

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||08:19
||It is supported by the National Mission on Education through ICT, MHRD, Government of India.

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||08:25
||More information on this mission is available at this link. 

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||08:29
||This is Madhuri Ganapathi from IIT Bombay, signing off. Thanks for joining.
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