Graphic software Can somebody recomend me a software(preferably free) to draw a graphic like this:

I have downloaded GeoGebra, but it seems I can't use it to draw such a graphic.

Inkscape is a general purpose open source vector graphics tool, available for all the standard platforms. I have used it for a few years.   It works moderately well with LaTeX, and the price is right.   Using Inkscape to produce a picture like the one you posted would be routine. Some fiddling might need to be done to get good positioning of labels. 
