From GeoGebra Manual
- With this tool you can create angles in different ways (also see command Angle):
- Click on three points to create an angle between these points. The second point selected is the vertex of the angle.
- Click on two segments to create the angle between them.
- Click on two lines to create the angle between them.
- Click on two vectors to create the angle between them.
- Click on a polygon to create all angles of this polygon.
Note: If the polygon was created by selecting its vertices in counter clockwise orientation, the Angle tool gives you the interior angles of the polygon.
Note: Angles are created in counter clockwise orientation. Therefore, the order of selecting these objects is relevant for the Angle tool. If you want to limit the maximum size of an angle to 180°, un-check Allow Reflex Angle on tab Basic of the Properties Dialog.