The movie demonstrates a solution of a typical construction problem: cut a segment into 2 equal segments. To solve the construction problem use a pen, pair of compasses and a ruler. To cut a segment into 2 equal segments make 2 circumferences with equal radiuses and centers at the ends of the segment. Connect crosssection points of the circumferences by a line CD. The crosspoint E of the line and the segment divides the segment into 2 equal segments.
