each image below links to a step‑by‑step GeoGebra applet, where you can move forwards and backwards through the construction or watch a short animation of how it unfolds. in some applets, the blue circular points are movable. these applets are also collected in this GeoGebra book.
regular octagon, given the large diagonal
regular octagon, given the edge length #01
regular octagon, given the edge length #02
moving geometry 