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Re: [EMHL] Re: Morley's double miracle

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  • Nikolaos Dergiades
    Dear Gilles You are right. Sketchpad and perhaps Cabri (I don t know it) are very good programs as visual constructors of geometric figures driven by the mouse
    Message 1 of 10 , Feb 24, 2002
      Dear Gilles

      You are right. Sketchpad and perhaps Cabri
      (I don't know it)
      are very good programs as visual constructors
      of geometric figures driven by the mouse but
      the precision I think is very bad.
      I would like to have a program that would be
      a combination of Sketchpad and Maple V that
      has very good precision and ability of symbolic
      (not only float point) calculations.

      You are right because I have I a proof that the
      opposite incenters I1, I'1and the B'C' side of Morley's
      triangle are not perpendicular. Only in the case that
      cos(x/2)sin(60+x) = cos(y/2)cos(z/2) where
      x=A/3 y=B/3 z=C/3 it is true, if I don't have an error
      in my calculations.

      The same I think (I have not a proof) for the lines
      I1I'1, I2I'2, I3I'3. I think they are not concurrent.

      Best regards
      Nikos Dergiades
      -----������ ������-----
      ���: Boutte Gilles <g.boutte@...>
      ����: Hyacinthos@yahoogroups.com <Hyacinthos@yahoogroups.com>
      ����������: ������� 6, 2002 11:27 PM
      ����: Re: [EMHL] Re: Morley's double miracle


      Sorry, I don't have a proof, only the values of the angles with Cabri.

      Regards,

      Gilles

      > > I've made an accurate sketch with Cabri, which answers : lines through
      > > opposite incenters and sides of Morley's triangle are not perpendicular.
      > > I've drawn some triangles, for which the angles of theses lines are
      > from
      > > 89.8 to 90.1 !!!
      >
      > I didn't think of measuring the angle. I was just looking at it by eye.
      > I tried the same thing with Sketchpad and can confirm that the
      > angle varies from 89.8 to 90.1.
      >
      > I also took the 3 points of intersection of pairs of lines
      > joining opposite incenters and measured the area of the triangle
      > they form. To 3 decimal places, I get 0.000 all the time.
      > So the 3 lines _do_ look concurrent. Do we have a proof yet?




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    • rabinowitzstanley
      ... I didn t think of measuring the angle. I was just looking at it by eye. I tried the same thing with Sketchpad and can confirm that the angle varies from
      Message 2 of 10 , Mar 6, 2002
        > I've made an accurate sketch with Cabri, which answers : lines through
        > opposite incenters and sides of Morley's triangle are not perpendicular.
        > I've drawn some triangles, for which the angles of theses lines are from
        > 89.8 to 90.1 !!!

        I didn't think of measuring the angle. I was just looking at it by eye.
        I tried the same thing with Sketchpad and can confirm that the
        angle varies from 89.8 to 90.1.

        I also took the 3 points of intersection of pairs of lines
        joining opposite incenters and measured the area of the triangle
        they form. To 3 decimal places, I get 0.000 all the time.
        So the 3 lines _do_ look concurrent. Do we have a proof yet?
      • Boutte Gilles
        Sorry, I don t have a proof, only the values of the angles with Cabri. Regards, Gilles
        Message 3 of 10 , Mar 6, 2002
          Sorry, I don't have a proof, only the values of the angles with Cabri.

          Regards,

          Gilles

          > > I've made an accurate sketch with Cabri, which answers : lines through
          > > opposite incenters and sides of Morley's triangle are not perpendicular.
          > > I've drawn some triangles, for which the angles of theses lines are
          > from
          > > 89.8 to 90.1 !!!
          >
          > I didn't think of measuring the angle. I was just looking at it by eye.
          > I tried the same thing with Sketchpad and can confirm that the
          > angle varies from 89.8 to 90.1.
          >
          > I also took the 3 points of intersection of pairs of lines
          > joining opposite incenters and measured the area of the triangle
          > they form. To 3 decimal places, I get 0.000 all the time.
          > So the 3 lines _do_ look concurrent. Do we have a proof yet?
        • rabinowitzstanley
          ... The maple program you are looking for might be found at http://www.math.rutgers.edu/~zeilberg/PG/gt.html
          Message 4 of 10 , Mar 8, 2002
            > I would like to have a program that would be
            > a combination of Sketchpad and Maple V that
            > has very good precision and ability of symbolic
            > (not only float point) calculations.

            The maple program you are looking for might be found at
            http://www.math.rutgers.edu/~zeilberg/PG/gt.html
          • Alexander Bogomolny
            ... Dear Nikos and Hyacinthians: Even if they are, I still grope for the proof. Let s just summarize the configuration as I see it with regard to several
            Message 5 of 10 , Mar 8, 2002
              ndergiades wrote:
              >
              > The same I think (I have not a proof) for the lines
              > I1I'1, I2I'2, I3I'3. I think they are not concurrent.

              Dear Nikos and Hyacinthians:

              Even if they are, I still grope for the proof. Let's just
              summarize the configuration as I see it with regard to several
              present or plausible concurrencies in that configuration.

              There's triangle ABC and Morley's triangle A'B'C'. In each
              of the six smaller triangles we choose a point - the incenter
              or the circumcenter - and connect them to the opposite one.
              Let's then denote the points in triangles that share a single
              vertex with ABC as O_A, O_B, O_C, and in the triangles that
              share a single vertex with A'B'C' as Q_A, Q_B, Q_C. Then we
              have two more triangle: O_A O_B O_C (shortened to OOO) and,
              similarly, QQQ. So there are four triangles, and the question
              is which ones are perspective. The question could be extended
              from Morley's to a more general configuration of isogonal lines.

              #| triangle pair | perspective | isogonal | support
              | | | generalization |
              ---------------------------------------------------------------
              | | | |
              1| ABC/A'B'C' | yes | yes | (*)
              | | | |
              ---------------------------------------------------------------
              Incenter case
              ---------------------------------------------------------------
              | | | |
              2| ABC/OOO | yes | yes | :-)
              3| ABC/QQQ | yes | yes | (*)
              4| A'B'C'/OOO | yes | ? |
              5| A'B'C'/QQQ | ? | ? |
              6| OOO/QQQ | ? | ? |
              | | | |
              ---------------------------------------------------------------
              Circumcenter case
              ---------------------------------------------------------------
              | | | |
              7| ABC/OOO | no | no | Sketchpad, Cabri, Java
              8| ABC/QQQ | no | no | Sketchpad, Cabri, Java
              9| A'B'C'/OOO | yes | ? | :-)
              10| A'B'C'/QQQ | yes | ? | ;-)
              11| OOO/QQQ | yes | ? | N. Dergiades
              | | | |
              ---------------------------------------------------------------

              (*) This is a well known fact, see for example,
              http://www.cut-the-knot.com/triangle/Morley/Morley.html

              There is of course the fifth triangle A"B"C", that Antreas mentioned
              in one of the recent posts, which is perspective to ABC and A'B'C',
              and is an out standing case of the isogonal generalization.

              All the best,
              Alexander Bogomolny
            • Antreas P. Hatzipolakis
              Dear Alexander, Thanks for your table. I prefer figures rather than tables :-) A B C = Morley Triangle of ABC. A / / / / / C B / A
              Message 6 of 10 , Mar 8, 2002
                Dear Alexander,

                Thanks for your table.

                I prefer figures rather than tables :-)

                A'B'C' = Morley Triangle of ABC.

                A
                /\
                / \
                / \
                / \
                / C' B' \
                / A' \
                / \
                B--------------C

                Denote:

                Ia, Ib, Ic : Incenters of AB'C', BC'A', CA'B', resp.

                I'a, I'b, I'c : Incenters of A'BC, B'CA, C'AB, resp.

                Oa, Ob, Oc : Circumcenters of AB'C', BC'A', CA'B', resp.

                O'a, O'b, O'c : Circumcenters of A'BC, B'CA, C'AB, resp.

                Ha, Hb, Hc : Orthocenters of AB'C', BC'A', CA'B', resp.

                H'a, H'b, H'c : Orthocenters of A'BC, B'CA, C'AB, resp.


                Perspectivities and Not:

                1. ABC, IaIbIc: Perspective
                [Perspector: I of ABC]

                2. ABC, HaHbHc : Not perspective

                3. ABC, OaObOc : Not perspective

                4. ABC, I'aI'bI'c : Perspective
                [Baryc. Perspector: (1/(cotA - cot(A/6)) ::) ]

                5. ABC, H'aH'bH'c : Not-Perspective

                6. ABC, O'aO'bO'c : Not-Perspective

                -----------

                1'. A'B'C', IaIbIc: Perspective
                [Baryc. Perspector wrt A'B'C': ((cot60 + cot(30 + (A/6)) ::)
                wrt ABC ?]

                2'. A'B'C', HaHbHc : Perspective
                [Baryc. Perspector wrt A'B'C': (1/(cot60 + cot(30 - (A/3)) ::)
                wrt ABC ?]

                3'. A'B'C', OaObOc : Perspective
                [ Perspector : the center of A'B'C' = X_356 ]

                4'. A'B'C', I'aI'bI'c : Not-Perspective

                5'. A'B'C', H'aH'bH'c : Not-Perspective

                6'. A'B'C', O'aO'bO'c : Perspective
                [ Perspector : the center of A'B'C' = X_356 ]

                -----------

                a. ABC, A'B'C' : Perspective
                [ Perspector X_357 ]

                b. IaIbIc, I'aI'bI'c : ???
                [I have computed the normals of the points with respect to A'B'C'
                but I don't know if the det. of the matrix of the lines IaI'a, etc,
                is zero or not]

                c. OaObOc, O'aO'bO'c : Perspective
                [ Perspector : the center of A'B'C' = X_356 ]

                d. HaHbHc, H'aH'bH'c : ???

                For the above Not-perspectivities there are simple proofs
                (not just geometry programs evidences)


                Good Night!

                Antreas
              • Alexander Bogomolny
                ... I guess tables are too square. But I was wrong in another respect. While triangle A B C is of course a specific isogonal case, we may consider it in its
                Message 7 of 10 , Mar 8, 2002
                  Dear Antreas:

                  > Thanks for your table.
                  >
                  > I prefer figures rather than tables :-)

                  I guess tables are too square.

                  But I was wrong in another respect. While
                  triangle A"B"C" is of course a specific
                  isogonal case, we may consider it in its
                  own right together with A'B'C'. Then
                  the table/list may be expanded.

                  > 4. ABC, I'aI'bI'c : Perspective
                  > [Baryc. Perspector: (1/(cotA - cot(A/6)) ::) ]

                  It's also curious that the fact itself can be
                  proved in projective geometry, since the isogonal
                  conjugation is a perspectivity of the pencil of
                  lines through the vertex.

                  > For the above Not-perspectivities there are simple proofs
                  > (not just geometry programs evidences)

                  I am very curious to get an example when a result in Morley's
                  configuration does not generalize to the isogonal case.

                  Talking of which, in some sense Morley's configuration
                  generalizes that of Napoleon and is generalizable itself.

                  For a given triangle A'B'C', form triangles A'B'C, B'C'A and
                  C'A'B. How? For example,

                  1. Napoleon: All angles are 60 degrees.
                  2. Kiepert: Similar isosceles triangles.
                  3. Isogonal conjugation: the angles of the add-on triangles
                  that share a vertex are equal.

                  In all three cases the lines AA', BB' and CC' are concurrent.
                  Now, the same appears to be true if

                  4. (Angles) B'A'C = AC'B', A'C'B = CB'A', C'A'B = AB'C'

                  What is this case? What framework does it belong to?

                  > Good Night!
                  >

                  Good morning to you.

                  Alexander
                • Antreas P. Hatzipolakis
                  Dear Alexander, ... A f w C --------------B q / q / / / / / w / f A B
                  Message 8 of 10 , Mar 9, 2002
                    Dear Alexander,

                    [AB]:
                    > For a given triangle A'B'C', form triangles A'B'C, B'C'A and
                    > C'A'B. How? For example,
                    >
                    > 1. Napoleon: All angles are 60 degrees.
                    > 2. Kiepert: Similar isosceles triangles.
                    > 3. Isogonal conjugation: the angles of the add-on triangles
                    > that share a vertex are equal.
                    >
                    > In all three cases the lines AA', BB' and CC' are concurrent.
                    > Now, the same appears to be true if
                    >
                    > 4. (Angles) B'A'C = AC'B': = f, A'C'B = CB'A' := q, C'A'B = AB'C' := w
                    >
                    > What is this case? What framework does it belong to?
                    >

                    A




                    f w
                    C'--------------B'
                    q \ / q
                    \ /
                    \ /
                    \ /
                    \ /
                    \ /
                    w \ / f
                    A'
                    B C


                    ABC, A'B'C' are perspective <==>

                    cotB' + cotw cotC' + cotq cotA' + cotf
                    ------------ * ------------- * ------------- = 1
                    cotC' + cotf cotA' + cotw cotB' + cotq

                    In general, not true.

                    Special Cases: f = q = w or A' = B' = C' [= 60]


                    Antreas
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