The main feature of dynamic (or interactive) geometry is that you should be able change a geometrical object without changing the significant properties of the object. In the applet above, you can change the shapes but they are always a rectangle, rhombus, parallelogram and trapezium.
If you draw a rectangle on a paper, your rectangle is merely one example of a rectangle. If you draw a rectangle in GeoGebra by placing four points, you can destroy the rectangle by dragging one of these points.
If you want to make a rectangle as a construction, you must consider the significant properties of a rectangle. When the construction is done, you should be able to drag some of the vertices to change the rectangle without destroying the properties of the rectangle; your construction should pass the dragging test.
Rectangles and parallelograms
The tools Perpendicular Line and Parallel Line can be used to construct rectangles and parallelograms respectively. Make sure that you know how to use these tools.
Exercise 1 - Parallel and perpendicular
Make sure you know how to construct a line through a point parallel to a given line ( a line already present in the construction).
Make sure you know how to construct a line through a point perpendicular to a given line.
Make sure you know how to construct a line through a point perpendicular to a given line if the point is on the line, as in the picture to the right.
Exercise 2 - Rectangle
Make a rectangle as a construction. When the construction is done, you should be able to move the points to change the size and the appearance; the quadrilateral should still remain a rectangle when moving the points.
Exercise 3 - Parallelogram
Make a parallelogram as a construction. When the construction is done, you should be able to move to points to change the size and the appearance; the quadrilateral should still remain a parallelogram when moving the points.
software: List of interactive geometry software
some examples, not GeoGebra: http://www.gogeometry.com/geometry/dynamic_geometry.html
by Malin Christersson under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 Sweden License