Using
This chapter shows you how you can use for your lessons.

Construct the circle of Thales
The circle of Thales
The circle of Thales
Please, do the following:
Construct three points at (-2;0), (0;0) and (2;0) respectively.
Construct a circle around the point in the middle with the radius 2. The two other points are now located at the circumference of the circle.
Construct a point on the upper half of this circle.
Draw a triangle through this point an the ones on the left and the right on the circumference of the circle.
Measure the top angle.
If you move the point on the upper half of the circle, the angle will remain 90 deg.