# Theorem of Thales

- Author:
- Dustin Warren

- Topic:
- Geometry

1. Draw a line segment.
2. Create a semicircle from the two endpoints of the segment. (The Semicircle tool is in the circle toolbox)
3. Place a point on the semicircle. We'll call this point C.
4. Create a triangle with the two endpoints of the segment from step 1 and the point you placed in step 3.
5. Measure the angles of the resulting triangle.
6. Answer the question below the activity.

1. Draw a line segment.
2. Create a semicircle from the two endpoints of the segment. (In the circle toolbox)
3. Place a point on the semcircle.
4. Create a triangle with the two endpoints of the segment from step 1 and the point you placed in step 3.
5. Measure the angles of the resulting triangle.
6. Answer the question below the activity.

What is the angle of the inscribed angle? (The angle whose vertex is located on the arc of the semicircle.)

Drag point C around the arc of the semicircle. What do you notice about the angle whose vertex is at C?