

A351582


Decimal expansion of the root of cot(Pi/(s+1))  csc(Pi/s).


1



4, 4, 9, 5, 4, 7, 4, 7, 8, 8, 7, 5, 2, 8, 8, 9, 0, 1, 6, 0, 7, 1, 7, 2, 3, 7, 9, 6, 0, 2, 8, 9, 3, 2, 9, 9, 3, 6, 6, 9, 0, 5, 1, 5, 6, 1, 3, 5, 4, 8, 6, 0, 9, 5, 6, 5, 9, 8, 3, 0, 5, 6, 9, 5, 4, 3, 8, 8, 0, 7, 3, 9, 3, 3, 5, 0, 3, 7, 9, 2, 0, 2, 6, 9, 2, 4, 0, 5, 4, 9, 2, 6, 1, 9, 5, 4, 2, 5, 8, 1, 9, 4, 4, 3, 1, 7
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OFFSET

1,1


COMMENTS

For regular unitsided polygons with number of sides s >= 3, the sgon fits inside the (s+1)gon, and hence inside any tgon where t > s. For s = 3 and s = 4, this is verified by diagram. For s >= 5, it is verified by observing that the sgon's circumcircle is smaller than the (s+1)gon's incircle. The difference of the two circles' radii is negative for s <= 4 and positive for s >= 5, and changes sign at noninteger value s = 4.49547...
Diagrams demonstrating this property of regular sgons are interesting (see links).


LINKS



FORMULA

For integer values of s >= 3:
c(s) = circumcircle radius of unitsided regular sgon = csc(Pi/s) / 2,
i(s) = incircle radius of unitsided regular sgon = cot(Pi/s) / 2,
d(s) = i(s+1)  c(s),
d(s) <= 0 for s <= 4, d(s) > 0 for s >= 5.
For real values of s:
d(1) = infinity,
d'(s) > 0 for s > 1,
d(s) = 0 for s = 4.4954747887528...


EXAMPLE

4.4954747887528...


MAPLE

Digits:= 120:


MATHEMATICA

RealDigits[s /. FindRoot[Cot[Pi/(s + 1)] == Csc[Pi/s], {s, 4}, WorkingPrecision > 120]][[1]] (* Amiram Eldar, Feb 14 2022 *)


PROG

(PARI) solve(s=4, 5, cotan(Pi/(s+1))  1/sin(Pi/s)) \\ Michel Marcus, Feb 14 2022


CROSSREFS



KEYWORD



AUTHOR



STATUS

approved



