Challenge 24: Side-Angle-Side (SAS)
If two sides and the angle between them of one triangle are equal to the corresponding sides and angle between them of another triangle, then the two triangles are congruent.
In this challenge, you will have to copy an angle. You can copy an angle in dynamic geometry using the compass tool, but it is a bit more complicated than copying a segment.
Watch this YouTube clip: http://www.youtube.com/watch?v=qngWUFgyyHc if you did not already. It gives a clear view of one way to use GeoGebra to copy an angle using tools that are equivalent to traditional geometry construction with a physical straightedge (for making line segments) and compass (for making circles).