The Geometer's Sketchpad

The Geometer's Sketchpad is a popular commercial interactive geometry software program for exploring Euclidean geometry, algebra, calculus, and other areas of mathematics. It was created by Nicholas Jackiw. It is designed to run onWindows 95 or Windows NT 4.0 or later and Mac OS 8.6 or later (including Mac OS X). It also runs on Linux under Winewith a few bugs.[1]

Sketchpad 4 working with triangle trisectors 

Geometer's Sketchpad includes the traditional Euclidean tools of classical geometric constructions; that is, if a figure (such as thepentadecagon) can be constructed with compass and straight-edge, it can also be constructed using this program. However, the program also allows users to employ transformations to "cheat," creating figures impossible to construct under the traditional compass-and-straight-edge rules (such as the regular nonagon). Objects can also be animated. The program also allows the determination of the midpointand midsegments of objects.

Geometer's Sketchpad also allows one to measure lengths ofsegments, measures of angles, area, perimeter, etc. Some of the tools one can use include construct function, which allows the user to create objects in relation to selected objects. The transform function allows the user to create points in relation to objects, which include distance, angle, ratio, and others. With these tools, one can create numerous different objects, measure them, and potentially figure out hard-to-solve math problems.

You can downoad this program at: dynamicgeometry.com/

or download portable version at: Portable Geometer Sketchpad 4.07.exe