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Geometer’s Sketchpad – EXTRA CREDIT

 

TRIANGLE CENTERS

Long before the first pencil and paper, some curious person drew a triangle in the sand and a line from each vertex to the midpoint of the opposite side. Amazingly enough the three connecting lines met in a single point - a point of concurrency. If you try it right now, the same thing will happen, no matter what shape of triangle you start with. The special point is called the centroid of the triangle. Think of it as the first triangle center,  historically and conceptually.

Aside from the centroid, the ancient Greeks also were fascinated by three other triangle centers: the triangle's incenter, circumcenter, and orthocenter.  Centuries passed before a fifth triangle center surfaced: the Fermat point.  During the nineteenth century, more triangle centers entered the literature, and then the people didn't talk much about them for a period of time.  New triangle centers are once again popping out, often with the help of computers. In the 1980s, it seemed that all these special points shared some general properties that should form the basis for a formal definition of triangle center.

Here is a list of triangle centers discovered in the 20th-century:
Schiffler Point Exeter Point Parry Point
Congruent Isoscelizers Point Yff Center of Congruence Isoperimetric Point and Equal Detour Point
Ajima-Malfatti Points Apollonius Point Morley Centers
Hofstadter Points Equal Parallelians Point Bailey Point

And here are some classical triangle centers:
Centroid Incenter Steiner point Circumcenter Isodynamic points
Orthocenter Fermat Point Feuerbach point Napoleon points Nine-point center
Symmedian point Gergonne point Spieker center Mittenpunkt Nagel point

For extra credit:
(You may do as many as five different constructions – only 3 can be classical centers – the other two must be 20th century centers.  Each completed construction (as described below) is worth 5 points.  Only two constructions can be placed in any one grade category!)

1.       Pick a triangle center from the ones above. 

2.     Open a Word document, put your name at the top, and title your extra  credit the name of the triangle center that you plan to create.

3.     In the Word document, describe the triangle center that you will create- how it is to be constructed, any special properties that it has, and any interesting things about that center.

4.      Using Geometer's Sketchpad, construct a triangle and the center that you have chosen.  When you know how to make the sketch, record a script for your construction and save it to your disk.

5.      Copy your triangle center construction into your Word document.

6.      At the bottom of the document identify  :

  • the script's file name
  • the name of the file where the actual  construction can be found, and
  • the grade category that you want to put the points in.

7.    Hand in your print-out and your disk.

 

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