Question 17
A semicircle is described in the source as having radius AB. Draw the zigzag inside it so that its segments make the marked angle $\alpha$ with AB, as shown. Find $\alpha$.
Editorial correction: Although the Vietnamese text twice says “radius AB”, the figure makes AB the diameter. All marked acute angles are taken equal to α, as intended by the diagram.
Editorial correction: Although the Vietnamese text twice says “radius AB”, the figure makes AB the diameter. All marked acute angles are taken equal to α, as intended by the diagram.