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rcarlton88
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Posts: 7
Joined: August 1st, 2007, 2:47 am

n-gon question

January 14th, 2008, 8:29 pm

Suppose you start with a regular n-gon, where n is at least 5, and you draw in all the diagonals that don't pass through the center. this divides the region enclosed by the regular n-gon into several parts, one of which contains the center.What is the shape of the part containing the center? How do you know?What is the area of the part containing the center, as a function of n and of the area of the entire region.
 
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Advaita
Posts: 188
Joined: April 20th, 2005, 1:54 pm

n-gon question

January 14th, 2008, 9:32 pm

For even: Only look at the diagonals 2nd in sizeFor odd: Only look at largest diags.Next you realise that smaller diagonals cannot cut this piece. By symmetry it's a small n-gon... too tired to calc the area.So for 8-gon, draw from 0 to 3, 3 to 6, 6 to 1, 1 to 4, 4 to 7, 7 to 2, 2 to 5, 5 to 0.Gives a smaller 8gon
 
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benczur
Posts: 64
Joined: December 2nd, 2005, 2:03 am

n-gon question

January 15th, 2008, 12:51 pm

For the area, calculate the distance from the center to the sides of the small and large n-gon, take the ratio and square.Distance to the sides of large n-gon: R*cos(pi/n).Distance to the sides of small n-gon: R*sin(pi/n), if n even,R*sin(pi/2n), if n odd.Area of small n-gon as a fraction of large one's area:(tan(pi/n))^2, n even(sin(pi/2n)/cos(pi/n))^2, n odd.
 
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MCarreira
Posts: 1724
Joined: July 14th, 2002, 3:00 am

n-gon question

January 15th, 2008, 2:11 pm

In Mathematica:ngon[p_, q_] := Polygon[Table[{Cos[2 Pi k q/p], Sin[2 Pi k q/p]}, {k, p}]];vrtngon[p_, q_] := Table[{Cos[2 Pi k q/p], Sin[2 Pi k q/p]}, {k, p}];linesngon[p_, q_] := Tuples[vrtngon[p, q], 2];nocenterlinesngon[p_, q_] := Module[{lista, iguais, opostos}, lista = linesngon[p, q]; iguais = Map[(#[[1]] == #[[2]]) &, lista]; opostos = Map[(#[[1]] == -#[[2]]) &, lista]; Pick[lista, Map[Apply[And, #] &, Transpose[{Map[Not, iguais], Map[Not, opostos]}]]]];GraphicsGrid[ Transpose[{Table[ Graphics[Map[Line, nocenterlinesngon[n, 1]], ImageSize -> Medium], {n, 5, 12}]}]]
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