Often in printed diagrams, lines are trimmed to avoid clutter.
Also, the extensions of finite lines (segments) must often be drawn.
Here is a simple idea for how to make trimmed lines in Geogebra.
The additional elements can be easily eliminated, and the whole process wrapped up into a tool:
Update:
TOOL! (.ggt): [url]http://www.geogebratube.org/material/show/id/87348[/url]
And simplified construction: [url]http://www.geogebratube.org/material/show/id/87349[/url]
