GeoGebra gives us a useful platform for experimenting with mathematical objects. They can be algebraic objects, like graphs of functions. They can also be geometric figures like triangles, rectangles, or circles. When we "construct" these figures, we want to maintain certain features while others are allowed to change. We illustrate this construction process by creating a dynamic rectangle. We can change the lengths of the sides and the position of the vertices, but the right angles always stay.
