A15. The "Angle" tool. The acute angle
Draw an acute angle called alpha "α"
Two Rays sharing the end, the vertex, divide the plane into two regions called angles. In order to distinguish them, each region is given a name (a Greek letter alpha α, beta β, gamma γ, delta δ, epsilon ε... or from other alphabets a, b, c, d, e...) and a circular arch is drawn from ray to ray, centred at the vertex. An acute angle is greater than a null angle (0º) and lower than a right angle (90º).
1st. Activate the "Ray" tool 
and draw two rays. The first one with the origin in point "A" and running through point "B", the second with the same origin and running through 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). If the angle is greater than or equal to 90º, activate the "Move" tool 
and move the points until the angle becomes acute.
Second way: Activate the "Angle" tool and click on two rays. With the "Move" tool activated, move the points until the angle becomes acute.
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. The first one with the origin in point "A" and running through point "B", the second with the same origin and running through 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). If the angle is greater than or equal to 90º, activate the "Move" tool and move the points until the angle becomes acute.
Second way: Activate the "Angle" tool and click on two rays. With the "Move" tool activated, move the points until the angle becomes acute.
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.