## Circle Geometry - A Beginner's Guide to Geogebra

This Word document is a beginner's guide to Geogebra. Geogebra is a free dynamic geometry program available in both Windows and Mac format from
http://www.geogebra.org/cms/

This document gives a brief introduction to Geogebra in the context of circle geometry.
Thanks to David Crewe for sharing.

## Sum of the Exterior Angles of a Polygon

This is a neat look-see proof that the sum of the exterior angles of any polygon is 360 degrees.
http://www.ies.co.jp/math/java/geo/gaikaku/gaikaku.html

## The Angle Sum of a Triangle

Move the triangle by dragging the red point. What did you find?
http://www.ies.co.jp/math/java/geo/san180/san180.html

## Tesselation Town on Tile Island

An interactive introduction to tessellations.

http://www.mathcats.com/explore/tessellations/tesspeople.html

## Matching Game: Polygons

Click on two cards to turn them over. If they match, they are cleared from the board. If not, they remain on the board. How many turns will it take you to clear the board?

http://www.interactivestuff.org/match/maker.phtml?featured=1&id=14

Click on two cards to turn them over. If they match, they are cleared from the board. If not, they remain on the board. How many turns will it take you to clear the board?

http://www.interactivestuff.org/match/maker.phtml?featured=1&id=24

## Matching Game: 3-D Shapes

Click on two cards to turn them over. If they match, they are cleared from the board. If not, they remain on the board. How many turns will it take you to clear the board?

http://www.interactivestuff.org/match/maker.phtml?featured=1&id=15

## Coins and Equilateral Trianges

When the centres of any three coins lie in the corners of an equilateral triangle of some size, such coins form an equilateral coin triangle. How many equilateral coin triangles of different sizes can you count in the figure?

The object of the puzzle now is to remove the minimum number of coins so that no equilateral coin triangles remain. In other words, centres of any three coins among those that remained don't lie in the corners of an equilateral triangle.

http://www.puzzles.com/PuzzlePlayground/CoinsAndTriangles/CoinsAndTriang...

## Tangram Puzzles

Level one is a nice not-too-hard introduction to tangram puzzles. This puzzle at this level is good for the littlies, I think.

The higher levels are still reasonably easy.

http://www.channel4learning.net/sites/puzzlemaths/tangrams.shtml

## Shapes and Space

This excellent ActivBoard flipchart includes 15 Mathematical activities to teach the subject of shapes and space.

It covers a wide range of areas such as transformations & reflections, the properties of shapes and using quadrilaterals. Three thumbs up!

The flipchart can be found here:
http://www.prometheanplanet.com/uk/server/show/ConResource.13733

If you are not yet a member of Promethean Planet, you will first have to register here:
http://www.prometheanplanet.com/uk/server/show/nav.914

If you want to view the activities and have some interactivity with them, but you don't have the ActivStudio software, you can download the free Viewer from here:
http://www.mypromethean.com/uk/server/show/ConWebDoc.2974