This is the fifth post of the GeoGebra 4.0 Sneak Peek Series.
One of the major enhancements of GeoGebra 4.0 is the integration of Computer Algebra System (CAS). The GeoGebra CAS window can be viewed by clicking the View>CAS from the menu bar. The CAS toolbar includes the following tools as shown in the first figure: Evaluate (exact evaluation), Numeric (numeric evaluation; e.g. sin(1)), Keep Input, Factor, Expand, Substitute, Solve, and Differential/ Integral.
You can enter expressions/equations at the CAS window (see black texts below) and click the buttons at the toolbar to perform a command. The output of a command is shown in blue texts. Line 1, for example, used the Evaluate button to simplify 2x + 4x – 3y + 2y. » Read more
An excellent presentation and tutorial by Dr. Linda Fahlberg about Wikispaces and GeoGebra.