Geogebra/C2/Angles-and-Triangles-Basics/English-timed

Time	Narration
00:00	Hello Everybody. Welcome to the Geogebra tutorial Angles and Triangles Basics.
00:06	If this is the first time you are using Geogebra, please see the Introduction to Geogebra tutorial on the spoken tutorial website.
00:14	To get started with Geogebra, I am using the Linux operating system Ubuntu Version 10.04 LTS and Geogebra Version 3.2.40.0.
00:24	The objective of this tutorial is to verify that the sum of the interior angles of a triangle is always 180 degrees, using Geogebra.
00:33	In this tutorial, we will learn to use the tools Polygon, Angle, Insert Text.
00:42	Now first, select the 'Polygon' tool. To draw a polygon, in this case a triangle, select the three vertices by clicking on the drawing pad. Then click on the first vertex.
00:57	To measure the interior angles of the triangle, select the 'Angle' tool. You can measure the angle in two ways. Click in clockwise the three vertices A, B then C. This measures the angle ABC named alpha.
01:15	The second way is to select the line segments that form the angle. Select segment a and segment b, this time anti-clockwise to get angle BCA named beta.
01:27	Similarly, CAB will measure the angle gamma.
01:35	Note all angles are named according to standard mathematical convention as Greek alphabets.
01:41	Also if you select the vertices anti-clockwise like this , C B A, then the exterior angle is measured.
01:53	To add text to your drawing pad, use Insert Text Tool. Then click anywhere on the drawing pad, a text window appears.
02:07	Now to display angle ABC, I will type within double quotes, Angle ABC =, close double quotes, add + and then click on alpha. Click OK. So I get the value of Angle ABC.
02:28	Similarly, to do arithmetic, to display the sum of the interior angles of this triangle, click on the 'Insert Text' tool, click here on the drawing pad. Type, within double quotes, Sum of the interior angles of triangle ABC = close double quotes plus (+) open brackets type alpha + beta + gamma close brackets. And click OK. Now you see the sum displayed.
03:14	Next, select the Move tool and move the free objects, in this case the vertices A B or C, and you will notice that the sum of the interior angles is always 180 degrees.
03:32	My favorite part of this lesson is to show, how when all the three vertices are on a straight line, reduces two of the interior angles to zero and the third becomes 180 degrees like this, a straight angle.
03:52	Next, we will learn two more things, the drawing pad properties and how to delete an object in Geogebra.
04:04	First the drawing pad properties. Right click anywhere on the drawing pad and then click on Drawing Pad.
04:14	The Drawing Pad properties window opens. You can change the background colour of the drawing pad here.
04:20	You can change properties of the axes here, both the X axis and the Y axis here and you can change the properties of the grid here.
04:31	Some properties to note are, the unit you can add for the axis, the labels you can add for the axis, and the X axis to Y axis ratio.
04:43	When we are doing simple geometry we usually would like to keep it a 1:1 ratio.
04:49	When you close, all changes you have made will be saved.
04:54	Now, to delete an object on the drawing pad, move the mouse over the object. I will move the mouse over the external angle, right click. You will notice that the object name appears here and then click on Delete, then the object disappears.
05:15	Another way of deleting an object is to select the object on the algebra view, right click on it and say Delete.
05:25	Notice when I delete the angle gamma, this text also disappears. It's because it is dependent on the angle gamma.
05:35	If I want to undo what I've deleted, just Edit and click Undo or press Ctrl+ Z.
05:45	To delete multiple objects in Geogebra the easiest way to do it is to left click anywhere on the drawing pad, drag the mouse over all the objects you want to delete, undo the click, all the items are selected and then press 'Delete' on your keyboard.
06:05	Again let's undo this by clicking Undo.
06:10	Now, I would like to explain the syntax of the text once again.
06:17	Text that needs to appear as-is must be within double quotes ”” as seen in the example.
06:25	For values of Geogebra variables, use the variable name as seen in the algebra view without quotes.
06:34	To do arithmetic with the values use the variables within brackets ().
06:40	Finally, to concatenate or connect text use the + sign.
06:46	Next, we will just look at some ways of matching the colours of the angles and the text.
06:59	Now if I want to change the text colour I will right click and say Object Properties, go to Color and change the colour and say Close.
07:12	Now I can go to the angle here, right click , say Object Properties. I can choose the recent window here and click on this colour for an exact match.
07:26	Similarly, if I want to zoom in and zoom out I use the Zoom In here to zoom in and the Zoom Out option and click on the drawing pad to zoom out.
07:47	To change the angle unit, I can go to Options, Angle unit and change from Degrees to Radians.
08:02	So, just to recap, I know how to change the angle measure from radians to degrees, I can zoom in and zoom out.
08:15	Now to the ASSIGNMENT.
08:19	Draw to verify the exterior angle of a triangle is equal to the sum of the opposite interior angles.
08:28:	Do the following steps: Draw a triangle using the Polygon tool.
08:32	Extend any one of the sides using the line through Two points tool.
08:36	Use the Angle tool to measure the exterior angle and the opposite interior angles.
08:41	Use the Insert Text tool to display the results. Verify this by using the Move tool and moving the free objects.
08:49	I will show you what I have done. You just need to use the Move tool and then move the Free objects.
08:57	You will notice that the exterior angle is always equal to the sum of the interior opposite angles.
09:08	I would like to acknowledge the spoken tutorial project which is part of the talk to a teacher project.
09:14	It is supported by the National Mission on Education through ICT,MHRD Government of India.
09:20	You can see more information about this at this website.
09:24	Thank you. This is Bindu, signing off. Enjoy exploring Geogebra.

Contributors and Content Editors

Minal, PoojaMoolya, Pratik kamble, Sandhya.np14