A18. The “Angle” tool. The straight angle
Draw a straight angle called "α"
In GeoGebra it is very difficult to draw a right angle by moving points to the Graphics View, so a grid has been created in order to place points properly in the intersections. A straight angle is exactly 180º.
1st. Activate the "Ray" tool 
and draw two rays by placing the points on the crossings of the grid. The first one with the origin in point "A" and running through point "B" and the second one that begins at point "A" and runs through the point "C".
2nd. Name one ray "r" and the other one "s".
3rd. There are two ways to show the angle:
First way: Activate the "Angle" tool 
and click on three points that define the rays. (The second click must be on the vertex). Activate the "Move" tool 
and move the points until the angle becomes straight.
Second way: Activate the "Angle" tool and click on two rays. With the "Move" tool activated, move the points until the angle becomes straight.
The two curved arrows located in the upper right corner of the Graphics View allow you to reset the activity.
If the activity is correct, you will get 10 points automatically.
and draw two rays by placing the points on the crossings of the grid. The first one with the origin in point "A" and running through point "B" and the second one that begins at point "A" and runs through the point "C".
2nd. Name one ray "r" and the other one "s".
3rd. There are two ways to show the angle:
First way: Activate the "Angle" tool and click on three points that define the rays. (The second click must be on the vertex). Activate the "Move" tool and move the points until the angle becomes straight.
Second way: Activate the "Angle" tool and click on two rays. With the "Move" tool activated, move the points until the angle becomes straight.
The two curved arrows located in the upper right corner of the Graphics View allow you to reset the activity.
If the activity is correct, you will get 10 points automatically.