Essays about Number Theory: From Classical Topics to New Problems - Hardcoverby Franz Rothe (Author) For a regular 17 gon, the formulas above give the x coordinate of the first vertex in the upper half plane. The first formula goes back to Gauss. The second formula is obtained by a more elementary method, see pages 39 to 47 in this book. This method uses only the trigonometric addition theorem and some clever guesses. It needed some optimism to create this book about number theory. The proofs are gapless and readable, and