(* Sequence of calculations for regular 17-gon.*)
(* Generated by Ken Brakke (brakke@susqu.edu) using my ngon.c program.*)

a0 = -1.000000000000000

prod =  + 4*a0
a1 = (a0 + Sqrt[a0^2 - 4*prod])/2

prod =  + 4*a0
a2 = (a0 - Sqrt[a0^2 - 4*prod])/2

prod =  + 1*a0
a5 = (a1 - Sqrt[a1^2 - 4*prod])/2

prod =  + 1*a0
a6 = (a2 - Sqrt[a2^2 - 4*prod])/2

prod =  + 1*a6
a13 = (a5 + Sqrt[a5^2 - 4*prod])/2

x2 = a13/2
Print["Constructed x of vertex 2: ",x2]
shouldbe = N[Cos[2*2*Pi/17]]
Print["Calculated x of vertex 2:  ",shouldbe]