Image:Neusis-heptagon.png

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Geometric details: OPQR is a unit square. The arc centred on O through Q is drawn, as is the perpendicular bisector of OP. The en:Neusis construction involves finding unit interval AB through P with A on the perpendicular bisector and B on the arc. Angle PAO is the interior angle of a heptagon. The remainder of the construction can be carried out with ruler and compass. (Two of the vertices lie on the lines OR and PQ.)

1 Summary
2 Licensing
3 Metapost source
4 See also

[edit] Summary

Description	Neusis construction of a regular heptagon
Source	own work
Date	19 May 2006
Author	User:AndrewKepert
Permission	GFDL and CC. GPL source included

The en:MetaPost source below is a bit of a cheat.

[edit] Licensing

I, the author of this work, hereby publish it under the following licenses:

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

This file is licensed under the Creative Commons Attribution ShareAlike license versions 2.5, 2.0, and 1.0

You may select the license of your choice.

[edit] Metapost source

The Metapost source for this file. All done via command line on MacOSX:

Metapost (mpost command from teTeX)
\convertMPtoPDF TeX command from supp-pdf.tex, processed via pdfTeX
ghostscript to a png at 1200x1200.

I hereby make this source available under the GPL version 2 or later.

u=2cm;
path unitcircle;   unitcircle=fullcircle scaled 2u;
thick=1mm;
thin=0.25mm;
transform heptT;
def drawruler(expr p,q) =
    path ruler[];
    ruler0:=unitsquare xscaled abs(p-q) yscaled .1u rotated angle(q-p) shifted p;
    ruler1:=unitsquare yscaled 0.5 shifted 0.25up
        xscaled abs(p-q) yscaled .1u rotated angle(q-p) shifted p;
    fill ruler0 withcolor (1,1,.5);
    fill ruler1 withcolor (.9,.9,.3);
    draw ruler0 withpen pencircle scaled 0.25;
    enddef;
beginfig(77)
    pickup  pencircle scaled thin;
    z0=(0,0);      z0d=(0,.4u);
    z1=(-0.5u,0);  z1l=(.5u-u*sqrt(2),0);
    z2=(0.5u,0);
    z3=(.5u,-u);   z3u=(.5u,-u*sqrt(2));
    z4=(-.5u,-u);
    z5=(0,-u);
    z6=(0,whatever)=z1+whatever*dir(180/7);
    z7=z6-u*dir(180/7);
    drawruler(z6,z7);
    drawruler(z3,z4);
    for i = 0 upto 7:
        z[i]vtx=dir(360i/7);
    endfor;
    xxpart heptT= yypart heptT;
    xypart heptT=-yxpart heptT;
    for i = 6,7: z[i] = z[i]vtx transformed heptT; endfor
    draw (for i = 0 upto 6: z[i]vtx -- endfor cycle) transformed heptT dashed evenly withcolor blue;
    draw z1--z2--z3--z4--cycle;
    draw z1l--z1;
    draw z0d--z5;
    draw z2--z4 dashed evenly;
    draw z6--z7;
    label.urt("O",z2);
    label.ulft("A",z6);
    label.ulft("P",z1);
    label.llft("Q",z4);
    label.rt("R",z3);
    label.lft("B",z7);
    draw subpath (4,5) of unitcircle scaled (sqrt(2)) shifted z2;
    for i = 1,2,6,7,3,4:
        if known(x[i]):
            drawdot z[i] withpen pencircle scaled thick;
        fi
    endfor
endfig;    
bye