Altitudes and Orthocenters

(Assignment 8)


J. Matt Tumlin, Cara Haskins, and Robin Kirkham


An orthocenter (H) of a triangle is the point where the lines containing its altitudes are concurrent.





Now, construct triangles between the orthocenter and 2 of the vertices of the triangle.




As you can see, the orthocenters of the three triangles are the vertices of the original triangle.  Does this relationship hold true for triangle ABC whether it is acute, right, or obtuse? 


What would happen if one of the vertices of triangle ABC was moved to where the orthocenter (H) is located?


To use a script tool to find out, CLICK HERE!



Now construct the Circumcircles for DABC, DHBC, DHAC, and DHAB.



What can you say about the radii of the circumcircles?  Are they congruent?  Are you sure?


To use a script tool to move the points, CLICK HERE!



In conclusion some conjectures are:


      The radii of each circumcircle is exactly the same.


      All circumcircles pass through the orthocenter(H) of the original triangle ABC.


      A cube is formed by connecting the centers of the circumcircles with the orthocenter H.  To use a script tool, CLICK HERE!


      The area of the overlap of the circumcenters at each vertex is bisected by the altitudes of the original triangle.


      A second area of overlap of the circumcircles is bisected by the sides of the original triangles.


      We know that the perpendicular bisector that intersects each side of the original triangle and travels through the orthocenter also intersects one of the centers of the outside circumcircles.



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