The visual geometry calculator allows you to choose among different geometric objects and helps you to calculate the lengths, angles and areas of these from a minimum of parameters. You are free to specify any angles or lengths of your choice, and as soon as your entered values can be used to calculate other lengths or angles, these are automatically filled in by the application.
http://www.youtube.com/watch?v=tfETmwod1as
http://www.youtube.com/watch?v=tfETmwod1as