## 19636Re: A point related to a quadrilateral

Expand Messages
• Jan 1, 2011
• 0 Attachment
Dear Jean-Pierre,

> For k =1,2,3,4, T_k is the triangle with vertices the A_i except A_k; O_k is the circumcenter of T_k, (O_k) the circumcircle and B_k the isogonal conjugate of A_k wrt T_k
> Then the inverse of B_k in (O_k) doesn't depend on k and this point M is the center of the homothecy mapping O_1,O_2,O_3,O_4 to B_1,B_2,B_3,B_4.
> Is there a special name for this point M? Do you know some references?
> Friendly. Jean-Pierre

I do not know a special name for point M.
However I noticed this. Maybe you know it already.
Let T(A_1,A_2,A_3,A_4) = Transform A_1,A_2,A_3,A_4 --> O_1,O_2,O_3,O_4.
Then T^2(A_1,A_2,A_3,A_4) produces a quadrilateral homethetic with A_1,A_2,A_3,A_4 only rotated 180 degrees. Again Center of Homothecy = M.
T^4(A_1,A_2,A_3,A_4) produces a quadrilateral homothetic and with same orientation as A_1,A_2,A_3,A_4.

Best regards and a creative year to all Hyacinthists!

Chris van Tienhoven
• Show all 12 messages in this topic