## How to Get Started with GEX2.0

19may11

\begin{document} \maketitle \section{Introduction} If you have not already done so, you should download Micheal Hvidsten's Geometry Explorer (GEX2.0) as appropriate to your computer platform. The GEX1.0 which comes on a CD with your textbook is not adequate for this course. Why this is so is explained at length elsewhere. \section{Why don't we use KSEG?} Especially since there seems to be a lot of advice on using KSEG in the Advice section of the course. KSEG is a good product, but it cannot do non-Euclidean geometry. Also, it does not come with an extensive manual documenting its use. It is a very useful construction kit for other courses. Therefore there is careful documentation here for it. GEX comes with a very generous document for how to use it. You should download it and keep it handy on your computer. \section{What about GEX?} GEX is very \textbf{ geometrical} in its design. That is, Prof. Hvidsten has separated the GEX palette (see the advice on Palettes) into three sections. \subsection{Create Geometrical Objects} The first, labelled \textbf{ Create}. The only essential buttons here are the Chooser (the black arrow) and the Point creator. But for your convenience, he has provided creators for the Circle, Segment, Ray, and Line. These all depend on two points, and could be constructed by creating two points, and then passing to the Construct buttons. So don't get confused by the fact that there are two buttons with the picture of a 2-point segment on them. They are located in different groups. \subsection{Construct Geometrical Objects} Given two geometrical objects, new objects can be constructed, which subsequently depend on the initial ones. Thus, if you move one of the end points of segment with the Chooser, the segment follows along. The construction does not fall apart. Experimenting witht these tools is the fastest way to learn GEX. \subsection{Transform Geometrical Objects} Certain point transformations in the plane, whether it is the Euclidean on a non-Euclidean plane, apply to any and all chosen objects. But the nature of the transformation must first be determined. For a translation, you'll need a vector. And a vector is best defined by two points, a first and a last point. The second point is the arrowhead on the vector. For a rotation, you'll need a point and an angle. And so forth. \section{The Wiggle Test} It is possible to construct a figure carelessly, disregarding the geometrical principles. So, you don't guess where the midpoint of a segment is located. You must construct it. (There is a button for that.) And, you can tell that you've done a proper construction, by moving some initial points (the ones you created at the start.) If the figure continues to illustrate the same geometrical principles, you have done it correctly. \end{document}