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Conference rusure::math

Title:Mathematics at DEC
Moderator:RUSURE::EDP
Created:Mon Feb 03 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:2083
Total number of notes:14613

809.0. "<><><> A trisected circle ... <><><>" by KEEPER::KOSTAS (He is great who confers the most benefits.) Thu Dec 24 1987 01:42

    Hello,
    
          How can a circle be divided into three equal parts?
    
    Enjoy,
    
    Kostas
    
T.RTitleUserPersonal
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809.1Equal area, or same shape, too?ZFC::DERAMOFrustrated personal name composerThu Dec 24 1987 14:3613
     What about dividing it up this way, where all three angles
     are supposed to be 120 degrees:

                                      |
                                      |
                                      |
                           center --> |
                                     / \
                                    /   \
                                   /     \
                                  /       \

     Dan
809.2Straightedge/compass (no proof)SMURF::JMARTINJoseph A. Martin, ULTRIX kernelThu Dec 24 1987 15:4012
 1) Inscribe a couple non-parallel chords.
 2) Construct their perpendicular bisectors.  Where the bisectors intersect
    is the center.
 3) Set compass from center to circumference.
 4) Mark a point on the circumference.
 5) Pivot the compass on this point and mark the point intersected by
    other leg.
 6) Repeat the above pivoting on the new point, proceeding around the
    circle until you reach the point marked in 4).

The circle is now divided into six equal parts and thus into three as well.
--Joe
809.3Let's have two categories for these ...KEEPER::KOSTASHe is great who confers the most benefits.Mon Dec 28 1987 00:1016
    re. .1, .2
    
    We could have two categories: 1) One in which we have both equal
    areas and identical shapes, and 2) one in which we have equal areas
    but not identical shapes.
    
    Both reply .1 and .2 are of the 1st categorie. I know a few more
    for the 1st categorie, namely the Chinese Kung Fu symbol (Yin Yang).
    This symbol divides the circle in two equal parts of equal shapes.

    And one for category 2 which similar to the Yin Yang but divides
    the circle in three equal parts of diferent shapes.
    
    /Kostas

    
809.4Easier SolutionLABC::FRIEDMANTue Jan 05 1988 17:443
    
    1)  Purchase a Mercedes-Benz.
    2)  Look at its insignia.
809.5CLT::GILBERTBuilderWed Jan 06 1988 14:255
    The circle of radius r can be divided into three parts having equal area
    with two parallel lines.  The lines are at distance x from the center of
    the circle, where x is a solution to:

	arccos(x/r) - (x/r) * sqrt(1 - (x/r)^2) = pi / 3