Math Photo: Parallel Lines Make Congruent Segments

Here’s a demonstration of a theorem of elementary geometry:  if parallel lines divide one transversal into congruent parts, then they divide all transversals into congruent parts.

Here, it’s easy to see that the top rail, the one perpendicular to the parallel posts, is divided into equal parts by the vertical posts.  So the angled segments are divided into congruent parts as well.