Octadecagon Octadecagon An octadecagon (or octakaidecagon) or 18-gon is an eighteen-sided polygon. A "regular octadecagon" has a Schläfli symbol {18} and can be constructed as a quasiregular truncated enneagon, t{9}, which alternates two types of edges. As 18 = 2 × 3, a regular octadecagon cannot be constructed using a compass and straightedge. However, it is constructible using neusis, or an angle trisection with a tomahawk. The following approximate construction is very similar to that of the enneagon, as an octadecagon can be constructed as a truncated enneagon. It is also feasible with exclusive use of compass and straightedge. The "regular
Hampton Sides a BA in history. Sides lives in Santa Fe, New Mexico, with his wife Anne Goodwin Sides, a journalist and former NPR editor, and their three boys, all soccer players. He is a past fellow of Yaddo, the MacDowell Colony, and the Japan Society, and an Edwards Media Fellow at Stanford University. He is an advisory board member of the Mayborn Literary Nonfiction Conference. Sides has guest-lectured at Columbia, Yale, Stanford, SMU, Colorado College, the Autry National Center of the American West, the American Embassy in Manila, Rehoboth Christian School, and the National World War II Museum, among other venues